net: libertas: inherit addr_assign_type along with dev_addr

A device inheriting a random or set address should reflect this in
its addr_assign_type.

Acked-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: David S. Miller <davem@davemloft.net>