Implemented MIP stack http_fetch()

This approach used tuntap driver for Linux/Unices

mip/mip.c

@@ -478,7 +478,7 @@ static size_t tx_tcp(struct mip_if *ifp, uint32_t dst_ip, uint8_t flags,
   struct ip *ip = tx_ip(ifp, 6, ifp->ip, dst_ip, sizeof(struct tcp) + len);
   struct tcp *tcp = (struct tcp *) (ip + 1);
   memset(tcp, 0, sizeof(*tcp));
-  memmove(tcp + 1, buf, len);
+  if (buf != NULL && len) memmove(tcp + 1, buf, len);
   tcp->sport = sport;
   tcp->dport = dport;
   tcp->seq = seq;
@@ -845,6 +845,11 @@ void mip_init(struct mg_mgr *mgr, struct mip_if *ifp) {
   }
 }
 
+void mip_free(struct mip_if * ifp) {
+    free((char *)ifp->rx.ptr);
+    free((char *)ifp->tx.ptr);
+}
+
 int mg_mkpipe(struct mg_mgr *m, mg_event_handler_t fn, void *d, bool udp) {
   (void) m, (void) fn, (void) d, (void) udp;
   MG_ERROR(("Not implemented"));

mip/mip.h

@@ -50,6 +50,7 @@ struct mip_if {
 };
 
 void mip_init(struct mg_mgr *, struct mip_if *);
+void mip_free(struct mip_if *);
 
 extern struct mip_driver mip_driver_stm32;
 extern struct mip_driver mip_driver_enc28j60;