macvlan: fix the problem when mac address changes for passthru mode

The macvlan dev should always have the same mac address like lowerdev
when in the passthru mode, change the mac address alone will break the
work mechanism, so when the lowerdev or macvlan mac address changes,
we should propagate the changes to another dev.

v1->v2: Allow macvlan dev to change mac address for passthru mode and propagate to
	lowerdev.

v2->v3: Don't set the mac address to the lower dev's unicast address for
	passthru mode when mac address changes.

Signed-off-by: Ding Tianhong <dingtianhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>