Merge branch 'macvlan-uaf'

Ziyang Xuan says:

====================
net: macvlan: fix potential UAF problem for lowerdev

Add the reference operation to lowerdev of macvlan to avoid
the potential UAF problem under the following known scenario:

Someone module puts the NETDEV_UNREGISTER event handler to a
work, and lowerdev is accessed in the work handler. But when
the work is excuted, lowerdev has been destroyed because upper
macvlan did not get reference to lowerdev correctly.

In addition, add net device refcount tracker to macvlan.
====================

Signed-off-by: David S. Miller <davem@davemloft.net>