bridge: Set vlan_features to allow offloads on vlans.

When vlan device is configured on top of the brige, it does
not support any offload capabilities because the bridge
device does not initiliaze vlan_fatures.  Set vlan_fatures to
be equivalent to hw_fatures.

Signed-off-by: Vlad Yasevich <vyasevic@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>