bridge: convert br_features_recompute() to ndo_fix_features

Note: netdev_update_features() needs only rtnl_lock as br->port_list
is only changed while holding it.

Signed-off-by: Michał Mirosław <mirq-linux@rere.qmqm.pl>
Signed-off-by: David S. Miller <davem@davemloft.net>