Added function netconn_free(), which deallocates all mboxes and frees the netconn (to be used from different places) - the PCB is not freed!

src/include/lwip/api_msg.h

@@ -149,6 +149,7 @@ void do_gethostbyname(void *arg);
 #endif /* LWIP_DNS */
 
 struct netconn* netconn_alloc(enum netconn_type t, netconn_callback callback);
+void netconn_free(struct netconn *conn);
 
 #ifdef __cplusplus
 }