[PATCH] net: allow netif_carrier to be called safely from IRQ

As reported by Ben Greer and Froncois Romieu. The code path in 
the netif_carrier code leads it to try and disable
a late workqueue to reenable it immediately
netif_carrier_on
-> linkwatch_fire_event
   -> linkwatch_schedule_work
      -> cancel_delayed_work
         -> del_timer_sync  

If __cancel_delayed_work is used instead then there is no
problem of waiting for running linkwatch_event.

There is a race between linkwatch_event running re-scheduling
but it is harmless to schedule an extra scan of the linkwatch queue.

Signed-off-by: Stephen Hemminger <redacted>

--- a/net/core/link_watch.c	2011-07-22 15:25:31.027533604 -0700
+++ b/net/core/link_watch.c	2011-07-22 15:31:27.531520028 -0700

@@ -126,7 +126,7 @@ static void linkwatch_schedule_work(int
 		return;
 
 	/* It's already running which is good enough. */
-	if (!cancel_delayed_work(&linkwatch_work))
+	if (!__cancel_delayed_work(&linkwatch_work))
 		return;
 
 	/* Otherwise we reschedule it again for immediate execution. */