bridge: netlink: add support for port's multicast_router attribute

Add IFLA_BRPORT_MULTICAST_ROUTER to allow setting/getting port's
multicast_router via netlink.

Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/uapi/linux/if_link.h b/include/uapi/linux/if_link.h
index fcea39a..e3b6217 100644
--- a/include/uapi/linux/if_link.h
+++ b/include/uapi/linux/if_link.h
@@ -304,6 +304,7 @@
 	IFLA_BRPORT_FORWARD_DELAY_TIMER,
 	IFLA_BRPORT_HOLD_TIMER,
 	IFLA_BRPORT_FLUSH,
+	IFLA_BRPORT_MULTICAST_ROUTER,
 	__IFLA_BRPORT_MAX
 };
 #define IFLA_BRPORT_MAX (__IFLA_BRPORT_MAX - 1)