pppoe: drop PPPOX_ZOMBIEs in pppoe_flush_dev

pppoe: drop PPPOX_ZOMBIEs in pppoe_flush_dev

BugLink: http://bugs.launchpad.net/bugs/769042

[ Upstream commit ae07b0b221b6ab2edf9e3abd518aec6cd3f1ba66 ]

otherwise we loop forever if a PPPoE socket was set
to PPPOX_ZOMBIE state by a PADT message when the
ethernet device is going down afterwards.

Signed-off-by: Ulrich Weber <uweber@astaro.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Leann Ogasawara <leann.ogasawara@canonical.com>