Benefit from the fact that dev->addr_assign_type is set to NET_ADDR_PERM
in case the device has permanent address.

This also fixes the problem that many drivers do not set perm_addr at
all.
Signed-off-by: NJiri Pirko <jiri@resnulli.us>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>