net/802/mrp: fix lockdep splat

commit fb745e9 ("net/802/mrp: fix possible race condition when
calling mrp_pdu_queue()") introduced a lockdep splat.

[   19.735147] =================================
[   19.735235] [ INFO: inconsistent lock state ]
[   19.735324] 3.9.2-build-0063 #4 Not tainted
[   19.735412] ---------------------------------
[   19.735500] inconsistent {IN-SOFTIRQ-W} -> {SOFTIRQ-ON-W} usage.
[   19.735592] rmmod/1840 [HC0[0]:SC0[0]:HE1:SE1] takes:
[   19.735682]  (&(&app->lock)->rlock#2){+.?...}, at: [<f862bb5b>]
mrp_uninit_applicant+0x69/0xba [mrp]

app->lock is normally taken under softirq context, so disable BH to
avoid the splat.

Reported-by: Denys Fedoryshchenko <denys@visp.net.lb>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: David Ward <david.ward@ll.mit.edu>
Cc: Cong Wang <amwang@redhat.com>
Tested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/802/mrp.c

@@ -871,10 +871,10 @@ void mrp_uninit_applicant(struct net_device *dev, struct mrp_application *appl)
 	 */
 	del_timer_sync(&app->join_timer);
 
-	spin_lock(&app->lock);
+	spin_lock_bh(&app->lock);
 	mrp_mad_event(app, MRP_EVENT_TX);
 	mrp_pdu_queue(app);
-	spin_unlock(&app->lock);
+	spin_unlock_bh(&app->lock);
 
 	mrp_queue_xmit(app);