net: bridge: fdb: eliminate extra port state tests from fast-path

When commit df1c0b8468b3 ("[BRIDGE]: Packets leaking out of
disabled/blocked ports.") introduced the port state tests in
br_fdb_update() it was to avoid learning/refreshing from STP BPDUs, it was
also used to avoid learning/refreshing from user-space with NTF_USE. Those
two tests are done for every packet entering the bridge if it's learning,
but for the fast-path we already have them checked in br_handle_frame() and
is unnecessary to do it again. Thus push the checks to the unlikely cases
and drop them from br_fdb_update(), the new nbp_state_should_learn() helper
is used to determine if the port state allows br_fdb_update() to be called.
The two places which need to do it manually are:
 - user-space add call with NTF_USE set
 - link-local packet learning done in __br_handle_local_finish()

Signed-off-by: Nikolay Aleksandrov <nikolay@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/bridge/br_input.c b/net/bridge/br_input.c
index f37b050..8944ceb 100644
--- a/net/bridge/br_input.c
+++ b/net/bridge/br_input.c
@@ -182,6 +182,7 @@ static void __br_handle_local_finish(struct sk_buff *skb)
 
 	/* check if vlan is allowed, to avoid spoofing */
 	if ((p->flags & BR_LEARNING) &&
+	    nbp_state_should_learn(p) &&
 	    !br_opt_get(p->br, BROPT_NO_LL_LEARN) &&
 	    br_should_learn(p, skb, &vid))
 		br_fdb_update(p->br, p, eth_hdr(skb)->h_source, vid, 0);