macvlan: Fix device ref leak when purging bc_queue

macvlan: Fix device ref leak when purging bc_queue

BugLink: http://bugs.launchpad.net/bugs/1688499
[ Upstream commit f6478218e6edc2a587b8f132f66373baa7b2497c ]

When a parent macvlan device is destroyed we end up purging its
broadcast queue without dropping the device reference count on
the packet source device.  This causes the source device to linger.

This patch drops that reference count.

Fixes: 260916dfb48c ("macvlan: Fix potential use-after free for...")
Reported-by: Joe Ghalam <Joe.Ghalam@dell.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>