[BRIDGE]: Fix device delete race.

This is a simpler fix for the two races in bridge device removal.
The Xen race of delif and notify is managed now by a new deleted flag.
No need for barriers or other locking because of rtnl mutex.

The del_timer_sync()'s are unnecessary, because br_stp_disable_port
delete's the timers, and they will finish running before RCU callback.

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>