Add an option to set source address for a BGP session.

When adding a BGP neighbour, one can set "update-source" (quagga syntax) to the
source IP address that will be used for that session.

Signed-off-by: Benjamin Cama <benoar@dolka.fr>

l2tpns.c

@@ -3564,7 +3564,8 @@ static void mainloop(void)
 		if (config->neighbour[i].name[0])
 			bgp_start(&bgp_peers[i], config->neighbour[i].name,
 				config->neighbour[i].as, config->neighbour[i].keepalive,
-				config->neighbour[i].hold, 0); /* 0 = routing disabled */
+				config->neighbour[i].hold, config->neighbour[i].update_source,
+				0); /* 0 = routing disabled */
 	}
 #endif /* BGP */