net: bridge: mcast: rename br_ip's u member to dst

Since now we have src in br_ip, u no longer makes sense so rename
it to dst. No functional changes.

v2: fix build with CONFIG_BATMAN_ADV_MCAST

CC: Marek Lindner <mareklindner@neomailbox.ch>
CC: Simon Wunderlich <sw@simonwunderlich.de>
CC: Antonio Quartulli <a@unstable.cc>
CC: Sven Eckelmann <sven@narfation.org>
CC: b.a.t.m.a.n@lists.open-mesh.org
Signed-off-by: Nikolay Aleksandrov <nikolay@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/if_bridge.h

@@ -25,7 +25,7 @@ struct br_ip {
 #if IS_ENABLED(CONFIG_IPV6)
 		struct in6_addr ip6;
 #endif
-	} u;
+	} dst;
 	__be16		proto;
 	__u16           vid;
 };