eth: reset addr_assign_type if eth_mac_addr() called

If eth_mac_addr() get called, usually if SIOCSIFHWADDR was
used to change the MAC of a ethernet device, reset the
addr_assign_type to NET_ADDR_PERM if the state was
NET_ADDR_RANDOM before. Reset the state since the MAC is
no longer random at least not from the kernel side.

v2: changed to bitops, removed if()

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