bridge: netlink: export port's bridge id

Add IFLA_BRPORT_BRIDGE_ID to allow getting the designated bridge id via
netlink.

Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/bridge/br_netlink.c b/net/bridge/br_netlink.c
index cad4050..c3e0b73 100644
--- a/net/bridge/br_netlink.c
+++ b/net/bridge/br_netlink.c
@@ -128,6 +128,7 @@
 		+ nla_total_size(1)	/* IFLA_BRPORT_PROXYARP */
 		+ nla_total_size(1)	/* IFLA_BRPORT_PROXYARP_WIFI */
 		+ nla_total_size(sizeof(struct ifla_bridge_id))	/* IFLA_BRPORT_ROOT_ID */
+		+ nla_total_size(sizeof(struct ifla_bridge_id))	/* IFLA_BRPORT_BRIDGE_ID */
 		+ 0;
 }
 
@@ -163,7 +164,9 @@
 	    nla_put_u8(skb, IFLA_BRPORT_PROXYARP_WIFI,
 		       !!(p->flags & BR_PROXYARP_WIFI)) ||
 	    nla_put(skb, IFLA_BRPORT_ROOT_ID, sizeof(struct ifla_bridge_id),
-		    &p->designated_root))
+		    &p->designated_root) ||
+	    nla_put(skb, IFLA_BRPORT_BRIDGE_ID, sizeof(struct ifla_bridge_id),
+		    &p->designated_bridge))
 		return -EMSGSIZE;
 
 	return 0;