bridge: do not call setup_timer() multiple times

commit 9f00b2e7cf24 ("bridge: only expire the mdb entry when query is
received") added a nasty bug as an active timer can be reinitialized.

setup_timer() must be done once, no matter how many time mod_timer()
is called. br_multicast_new_group() is the right place to do this.

Reported-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Diagnosed-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Tested-by: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Cc: Cong Wang <amwang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/bridge/br_multicast.c

@@ -619,6 +619,9 @@ rehash:
 	mp->br = br;
 	mp->addr = *group;
 
+	setup_timer(&mp->timer, br_multicast_group_expired,
+		    (unsigned long)mp);
+
 	hlist_add_head_rcu(&mp->hlist[mdb->ver], &mdb->mhash[hash]);
 	mdb->size++;
 
@@ -1126,7 +1129,6 @@ static int br_ip4_multicast_query(struct net_bridge *br,
 	if (!mp)
 		goto out;
 
-	setup_timer(&mp->timer, br_multicast_group_expired, (unsigned long)mp);
 	mod_timer(&mp->timer, now + br->multicast_membership_interval);
 	mp->timer_armed = true;
 
@@ -1204,7 +1206,6 @@ static int br_ip6_multicast_query(struct net_bridge *br,
 	if (!mp)
 		goto out;
 
-	setup_timer(&mp->timer, br_multicast_group_expired, (unsigned long)mp);
 	mod_timer(&mp->timer, now + br->multicast_membership_interval);
 	mp->timer_armed = true;