Revert "netfilter: conntrack: fix race in __nf_conntrack_confirm against get_next_corpse"

This reverts commit 88fd8709858b9cd94e2d28b4b3cac4b752f0683a which was
commit 5195c14c8b27cc0b18220ddbf0e5ad3328a04187 upstream, which was
reverted in commit 43612d7c04f1a4f5e60104143918fcdf018b66ee.

Reported-by: Pablo Neira Ayuso <pablo@netfilter.org>
Cc: Daniel Borkmann <dborkman@redhat.com>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Linux 3.17.6