In the old days, we used to access dev->master in __netif_receive_skb()
in a rcu_read_lock section.

So one synchronize_net() call was needed in netdev_set_master() to make
sure another cpu could not use old master while/after we release it.

We now use netdev_rx_handler infrastructure and added one
synchronize_net() call in bond_release()/bond_release_all()

Remove the obsolete synchronize_net() from netdev_set_master() and add
one in bridge del_nbp() after its netdev_rx_handler_unregister() call.

This makes enslave -d a bit faster.
Signed-off-by: NEric Dumazet <eric.dumazet@gmail.com>
CC: Jiri Pirko <jpirko@redhat.com>
CC: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>