Introduce MG_NET_IF var, replaces MG_NET_IF_*

Possible values:
  MG_NET_IF_SOCKET (1) - traditional BSD socket API
  MG_NET_IF_SIMPLELINK (2) - TI's SimpleLink socket interface
  MG_NET_IF_LWIP_LOW_LEVEL - a net_if implementation that uses LWIP's
    low-level API, when LWIP_SOCKET is not available.

PUBLISHED_FROM=a5c0aebb7b6bdb1f1f4cb3210763d16f3ab5e133

mongoose.h

@@ -75,6 +75,10 @@
 
 #endif /* !defined(CS_PLATFORM) */
 
+#define MG_NET_IF_SOCKET 1
+#define MG_NET_IF_SIMPLELINK 2
+#define MG_NET_IF_LWIP_LOW_LEVEL 3
+
 /* Amalgamated: #include "common/platforms/platform_unix.h" */
 /* Amalgamated: #include "common/platforms/platform_windows.h" */
 /* Amalgamated: #include "common/platforms/platform_esp_lwip.h" */
@@ -270,6 +274,10 @@ typedef struct _stati64 cs_stat_t;
 #define MG_ENABLE_HTTP_CGI 1
 #endif
 
+#ifndef MG_NET_IF
+#define MG_NET_IF MG_NET_IF_SOCKET
+#endif
+
 #endif /* CS_PLATFORM == CS_P_WINDOWS */
 #endif /* CS_COMMON_PLATFORMS_PLATFORM_WINDOWS_H_ */
 #ifdef MG_MODULE_LINES
@@ -392,6 +400,10 @@ typedef struct stat cs_stat_t;
 #define MG_ENABLE_HTTP_CGI 1
 #endif
 
+#ifndef MG_NET_IF
+#define MG_NET_IF MG_NET_IF_SOCKET
+#endif
+
 #endif /* CS_PLATFORM == CS_P_UNIX */
 #endif /* CS_COMMON_PLATFORMS_PLATFORM_UNIX_H_ */
 #ifdef MG_MODULE_LINES
@@ -448,12 +460,14 @@ unsigned long os_random(void);
 #define random os_random
 
 #ifndef RTOS_SDK
-#define MG_NET_IF_LWIP
+#define MG_NET_IF MG_NET_IF_LWIP_LOW_LEVEL
 struct mg_mgr;
 struct mg_connection;
 uint32_t mg_lwip_get_poll_delay_ms(struct mg_mgr *mgr);
 void mg_lwip_set_keepalive_params(struct mg_connection *nc, int idle,
                                   int interval, int count);
+#else
+#define MG_NET_IF MG_NET_IF_SOCKET
 #endif
 
 #ifndef CS_ENABLE_STDIO
@@ -482,7 +496,7 @@ void mg_lwip_set_keepalive_params(struct mg_connection *nc, int idle,
 #include <string.h>
 #include <time.h>
 
-#define MG_SOCKET_SIMPLELINK 1
+#define MG_NET_IF MG_NET_IF_SIMPLELINK
 #define MG_DISABLE_SYNC_RESOLVER 1
 
 /*
@@ -536,7 +550,7 @@ int inet_pton(int af, const char *src, void *dst);
 #include <sys/time.h>
 #endif
 
-#define MG_SOCKET_SIMPLELINK 1
+#define MG_NET_IF MG_NET_IF_SIMPLELINK
 #define MG_DISABLE_SYNC_RESOLVER 1
 
 /* Only SPIFFS supports directories, SLFS does not. */
@@ -671,7 +685,7 @@ struct dirent *readdir(DIR *dir);
 #include <sys/time.h>
 #endif
 
-#define MG_SOCKET_SIMPLELINK 1
+#define MG_NET_IF MG_NET_IF_SIMPLELINK
 #define MG_DISABLE_SYNC_RESOLVER 1
 
 /* Amalgamated: #include "common/platforms/simplelink/cs_simplelink.h" */
@@ -785,7 +799,7 @@ int _stat(const char *pathname, struct stat *st);
 #define CS_COMMON_PLATFORMS_SIMPLELINK_CS_SIMPLELINK_H_
 
 /* If simplelink.h is already included, all bets are off. */
-#if defined(MG_SOCKET_SIMPLELINK) && !defined(__SIMPLELINK_H__)
+#if MG_NET_IF == MG_NET_IF_SIMPLELINK && !defined(__SIMPLELINK_H__)
 
 #include <stdbool.h>
 
@@ -876,7 +890,7 @@ int sl_set_ssl_opts(struct mg_connection *nc);
 }
 #endif
 
-#endif /* defined(MG_SOCKET_SIMPLELINK) && !defined(__SIMPLELINK_H__) */
+#endif /* MG_NET_IF == MG_NET_IF_SIMPLELINK && !defined(__SIMPLELINK_H__) */
 
 #endif /* CS_COMMON_PLATFORMS_SIMPLELINK_CS_SIMPLELINK_H_ */
 #ifdef MG_MODULE_LINES
@@ -1032,6 +1046,10 @@ typedef unsigned int* uintptr_t;
 #define MG_ENABLE_FILESYSTEM 1
 #endif
 
+#ifndef MG_NET_IF
+#define MG_NET_IF MG_NET_IF_SOCKET
+#endif
+
 typedef struct _stati64 {
   uint32_t st_mtime;
   uint32_t st_size;
@@ -1423,10 +1441,6 @@ const char *c_strnstr(const char *s, const char *find, size_t slen);
 #define MG_DISABLE_RESOLVER 0
 #endif
 
-#ifndef MG_DISABLE_SOCKET_IF
-#define MG_DISABLE_SOCKET_IF 0
-#endif
-
 #ifndef MG_DISABLE_SYNC_RESOLVER
 #define MG_DISABLE_SYNC_RESOLVER 0
 #endif
@@ -1523,6 +1537,10 @@ const char *c_strnstr(const char *s, const char *find, size_t slen);
 #define MG_ENABLE_STDIO CS_ENABLE_STDIO
 #endif
 
+#ifndef MG_NET_IF
+#define MG_NET_IF MG_NET_IF_SOCKET
+#endif
+
 #ifndef MG_ENABLE_THREADS /* ifdef-ok */
 #ifdef _WIN32
 #define MG_ENABLE_THREADS 1
@@ -1592,7 +1610,7 @@ const char *c_strnstr(const char *s, const char *find, size_t slen);
 #ifdef __APPLE__
 #pragma GCC diagnostic ignored "-Wdeprecated-declarations"
 #endif
-#if !defined(MG_SOCKET_SIMPLELINK)
+#if MG_NET_IF != MG_NET_IF_SIMPLELINK
 #include <openssl/ssl.h>
 #endif
 #endif /* MG_ENABLE_SSL */
@@ -1673,7 +1691,7 @@ struct mg_connection {
   struct mbuf recv_mbuf;   /* Received data */
   struct mbuf send_mbuf;   /* Data scheduled for sending */
 #if MG_ENABLE_SSL
-#if !defined(MG_SOCKET_SIMPLELINK)
+#if MG_NET_IF != MG_NET_IF_SIMPLELINK
   SSL *ssl;
   SSL_CTX *ssl_ctx;
 #else
@@ -1950,7 +1968,7 @@ struct mg_connection *mg_connect_opt(struct mg_mgr *mgr, const char *address,
                                      mg_event_handler_t handler,
                                      struct mg_connect_opts opts);
 
-#if MG_ENABLE_SSL && !defined(MG_SOCKET_SIMPLELINK)
+#if MG_ENABLE_SSL && MG_NET_IF != MG_NET_IF_SIMPLELINK
 /*
  * Note: This function is deprecated. Please, use SSL options in
  * mg_connect_opt.
@@ -2376,7 +2394,8 @@ void mg_set_close_on_exec(sock_t);
  */
 void mg_conn_addr_to_str(struct mg_connection *nc, char *buf, size_t len,
                          int flags);
-#if !MG_DISABLE_SOCKET_IF /* Legacy interface. */
+#if MG_NET_IF == MG_NET_IF_SOCKET
+/* Legacy interface. */
 void mg_sock_to_str(sock_t sock, char *buf, size_t len, int flags);
 #endif