bridge: use list_for_each_entry() in netpoll functions

We don't delete 'p' from the list in the loop,
so we can just use list_for_each_entry().

Cc: David Miller <davem@davemloft.net>
Cc: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: Cong Wang <amwang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>