add callback function for hin2n to protect socket (#684)

include/n2n_typedefs.h

@@ -516,6 +516,9 @@ typedef struct n2n_edge_callbacks {
 
     /* Called periodically in the main loop. */
     void (*main_loop_period)(n2n_edge_t *eee, time_t now);
+
+    /* Called when a new socket to supernode is created. */
+    void (*sock_opened)(n2n_edge_t *eee);
 } n2n_edge_callbacks_t;
 
 typedef struct n2n_tuntap_priv_config {

src/edge_utils.c

@@ -219,6 +219,9 @@ int supernode_connect(n2n_edge_t *eee) {
             return -1;
         }
 
+        if(eee->cb.sock_opened)
+            eee->cb.sock_opened(eee);
+
         struct sockaddr_in sock;
         sock.sin_family = AF_INET;
         sock.sin_port = htons(eee->curr_sn->sock.port);