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

This reverts commit 5195c14c

.

If the conntrack clashes with an existing one, it is left out of
the unconfirmed list, thus, crashing when dropping the packet and
releasing the conntrack since golden rule is that conntracks are
always placed in any of the existing lists for traceability reasons.

Reported-by: Daniel Borkmann <dborkman@redhat.com>
Fixes: https://bugzilla.kernel.org/show_bug.cgi?id=88841
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>