socket_info: provide send callback for internal listeners

When a proto hooks on top of another proto to operate (such as
proto_ipsec is using proto_udp and proto_tcp listners), we need a hook
before sending a message out.

Author: razvancrainea

forward.h

@@ -102,7 +102,7 @@ static inline int msg_send( const struct socket_info* send_sock, int proto,
 	out_buff.len = len;
 	out_buff.s = buf;
 
-	/* determin the send socket */
+	/* determine the send socket */
 	if (send_sock==0)
 		send_sock=get_send_socket(0, to, proto);
 	if (send_sock==0){
@@ -119,6 +119,8 @@ static inline int msg_send( const struct socket_info* send_sock, int proto,
 
 	/* update the length for further processing */
 	len = out_buff.len;
+	if ((send_sock->flags & SI_INTERNAL) && send_sock->internal_proto != PROTO_NONE)
+		proto = send_sock->internal_proto;
 
 	if (protos[proto].tran.send(send_sock, out_buff.s, out_buff.len, to,id)<0){
 		get_su_info(to, ip, port);

socket_info.h

@@ -63,6 +63,7 @@ struct socket_info {
 	unsigned short workers;
 	struct scaling_profile *s_profile;
 	void *extra_data;
+	enum sip_protos internal_proto;
 
 	/* these are IP-level local/remote ports used during the last write op via
 	 * this sock (or a connection belonging to this sock). These values are