[core] store struct server * in struct connection

src/base.h

@@ -257,6 +257,7 @@ struct connection {
 	int async_callback;
 
 	log_error_st *errh;
+	server *srv;
 
 	void **plugin_ctx;           /* plugin connection specific config */
 

src/connections.c

@@ -1093,6 +1093,7 @@ connection *connection_accepted(server *srv, server_socket *srv_socket, sock_add
 
 		con = connections_get_new_connection(srv);
 		con->errh = srv->errh;
+		con->srv  = srv;
 
 		con->fd = cnt;
 		con->fdn = fdevent_register(srv->ev, con->fd, connection_handle_fdevent, con);