socket: Call data handler as long as handler takes data.

Reviewed-by: Andreas Schneider <asn@cryptomilk.org>

src/socket.c

@@ -283,10 +283,12 @@ int ssh_socket_pollcallback(struct ssh_poll_handle_struct *p, socket_t fd, int r
                 return -1;
             }
 			if(s->callbacks && s->callbacks->data){
+				do {
 					r= s->callbacks->data(buffer_get_rest(s->in_buffer),
 							buffer_get_rest_len(s->in_buffer),
 							s->callbacks->userdata);
 					buffer_pass_bytes(s->in_buffer,r);
+				} while (r > 0);
 				/* p may have been freed, so don't use it
 				* anymore in this function */
 				p = NULL;