macvlan: Change status when lower device goes down

Today macvlan ignores the notification when a lower device goes
administratively down, preventing the lack of connectivity from
bubbling up.

Processing NETDEV_DOWN results in a macvlan state of LOWERLAYERDOWN
with NO-CARRIER which should be easy to interpret in userspace.

2: lower: <BROADCAST,MULTICAST> mtu 1500 qdisc mq state DOWN mode DEFAULT group default qlen 1000
3: macvlan@lower: <NO-CARRIER,BROADCAST,MULTICAST,UP,M-DOWN> mtu 1500 qdisc noqueue state LOWERLAYERDOWN mode DEFAULT group default qlen 1000

Signed-off-by: Suresh Krishnan <skrishnan@arista.com>
Signed-off-by: Travis Brown <travisb@arista.com>
Signed-off-by: David S. Miller <davem@davemloft.net>