call mg_tcpip_free from mg_mgr_free()

src/net.c

@@ -247,6 +247,9 @@ void mg_mgr_free(struct mg_mgr *mgr) {
   if (mgr->epoll_fd >= 0) close(mgr->epoll_fd), mgr->epoll_fd = -1;
 #endif
   mg_tls_ctx_free(mgr);
+#if MG_ENABLE_TCPIP
+  if (mgr->ifp) mg_tcpip_free(mgr->ifp);
+#endif
 }
 
 void mg_mgr_init(struct mg_mgr *mgr) {

src/net_builtin.c

@@ -1,6 +1,6 @@
 #include "net_builtin.h"
 
-#if defined(MG_ENABLE_TCPIP) && MG_ENABLE_TCPIP
+#if MG_ENABLE_TCPIP
 #define MG_EPHEMERAL_PORT_BASE 32768
 #define PDIFF(a, b) ((size_t) (((char *) (b)) - ((char *) (a))))