net: handle addr_type of 0 properly

addr_type of 0 means that the type should be adopted from from_dev and
not from __hw_addr_del_multiple(). Unfortunately it isn't so and
addr_type will always be considered. Fix this by implementing the
considered and documented behavior.

Signed-off-by: Hagen Paul Pfeifer <hagen@jauu.net>
Signed-off-by: David S. Miller <davem@davemloft.net>