kernel: add missing in6_dev_put_clear call to an ipv6 network patch

kernel: add missing in6_dev_put_clear call to an ipv6 network patch

Fixes "unregister_netdevice: waiting for lo to become free. Usage count = 1"
messages which started appearing since the update to 4.4.103. That
problem was exposed by upstream commit 76da0704507bb ("ipv6: only call
ip6_route_dev_notify() once for NETDEV_UNREGISTER") backported to 4.4.x
branch in 2417da3f4d6bc.

Fixes: 2b664499cd622 ("kernel: bump 4.4 to 4.4.103 for 17.01")
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
(cherry picked from commit 58f7b5b96c301176d639540df4723c798af2a999)