macvlan: Propagate promiscuity setting to lower devices.

When a macvlan device is placed in promiscuous mode, it currently
just sets it's multicast mask to permissive, but doesn't change
the state of the lower device.  As a result, not all multicast
traffic can be received on such device.  Additionally, none of
a vlan traffic can be received on such device as well.
This patch propagates the promiscuous mode setting to lower device
so that lower device may receive all packets that macvlan may
be interested in.

Signed-off-by: Vladislav Yasevich <vyasevic@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>