igbvf: reset netdevice addr_assign_type if changed

Reset the state of addr_assign_type to NET_ADDR_PERM as soon as
the MAC get changed via .ndo_set_mac_address.

v2: use bitops to reset addr_assign_type

Signed-off-by: Danny Kukawka <danny.kukawka@bisect.de>
Signed-off-by: David S. Miller <davem@davemloft.net>