bonding: Don't hold lock when calling rtnl_unlock

Change bond_mii_monitor to not hold any locks when calling rtnl_unlock,
as rtnl_unlock can sleep (when acquring another mutex in netdev_run_todo).

Bug reported by Makito SHIOKAWA <mshiokawa@miraclelinux.com>, who
included a different patch.
Signed-off-by: NJay Vosburgh <fubar@us.ibm.com>
Signed-off-by: NJeff Garzik <jeff@garzik.org>

drivers/net/bonding/bond_main.c

@@ -2386,7 +2386,9 @@ void bond_mii_monitor(struct work_struct *work)
 		rtnl_lock();
 		read_lock(&bond->lock);
 		__bond_mii_monitor(bond, 1);
-		rtnl_unlock();
+		read_unlock(&bond->lock);
+		rtnl_unlock();	/* might sleep, hold no other locks */
+		read_lock(&bond->lock);
 	}
 
 	delay = ((bond->params.miimon * HZ) / 1000) ? : 1;