ethtool: set addr_assign_type to NET_ADDR_SET when addr is passed on create

In case user passed address via netlink during create, NET_ADDR_PERM was set.
That is not correct so fix this by setting NET_ADDR_SET.

Signed-off-by: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: David S. Miller <davem@davemloft.net>