bridge: fix hang on removal of bridge via netlink

Need to cleanup bridge device timers and ports when being bridge
device is being removed via netlink.

This fixes the problem of observed when doing:
 ip link add br0 type bridge
 ip link set dev eth1 master br0
 ip link set br0 up
 ip link del br0

which would cause br0 to hang in unregister_netdev because
of leftover reference count.

Reported-by: Sridhar Samudrala <sri@us.ibm.com>
Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Acked-by: Sridhar Samudrala <sri@us.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>