This patch fixes a netns leak.

Fixes: 93edb8c7 ("gtp: reload GTPv1 header after pskb_may_pull()")
Reported-by: NCong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: NPablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>