vswitchd: Inherit parents mac address for fake bridges

vswitchd: Inherit parents mac address for fake bridges

When adding a physical port to the main bridge the mac address
of the bridge is updated. We can do the same for fake bridges by
copying the mac address of the parent bridge.

There exists only one fake bridge per vlan, hence it is safe
to copy the mac address of the parent bridge.

Signed-off-by: Helmut Schaa <helmut.schaa@googlemail.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>