[BRIDGE]: use kzalloc

Use kzalloc versus kmalloc+memset. Also don't need to do
memset() of bridge address since it is in netdev private data
that is already zero'd in alloc_netdev.

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