bridge: fdb: converge fdb searching functions into one

Before this patch we had 3 different fdb searching functions which was
confusing. This patch reduces all of them to one - fdb_find_rcu(), and
two flavors: br_fdb_find() which requires hash_lock and br_fdb_find_rcu
which requires RCU. This makes it clear what needs to be used, we also
remove two abusers of __br_fdb_get which called it under hash_lock and
replace them with br_fdb_find().

Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/bridge/br_device.c b/net/bridge/br_device.c
index d208ee9..ea71513 100644
--- a/net/bridge/br_device.c
+++ b/net/bridge/br_device.c
@@ -79,7 +79,7 @@ netdev_tx_t br_dev_xmit(struct sk_buff *skb, struct net_device *dev)
 			br_multicast_flood(mdst, skb, false, true);
 		else
 			br_flood(br, skb, BR_PKT_MULTICAST, false, true);
-	} else if ((dst = __br_fdb_get(br, dest, vid)) != NULL) {
+	} else if ((dst = br_fdb_find_rcu(br, dest, vid)) != NULL) {
 		br_forward(dst->dst, skb, false, true);
 	} else {
 		br_flood(br, skb, BR_PKT_UNICAST, false, true);