inet: Add a count to struct inet_listen_hashbucket

This patch adds a count to the 'struct inet_listen_hashbucket'.
It counts how many sk is hashed to a bucket.  It will be
used to decide if the (to-be-added) portaddr listener's hashtable
should be used during inet[6]_lookup_listener().

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/inet_hashtables.h

@@ -111,6 +111,7 @@ struct inet_bind_hashbucket {
  */
 struct inet_listen_hashbucket {
 	spinlock_t		lock;
+	unsigned int		count;
 	struct hlist_head	head;
 };