[NETFILTER]: ctnetlink: make sure event order is correct

The following sequence is displayed during events dumping of an ICMP
connection: [NEW] [DESTROY] [UPDATE]

This happens because the event IPCT_DESTROY is delivered in
death_by_timeout(), that is called from the icmp protocol helper
(ct->timeout.function) once we see the reply.

To fix this, we move this event to destroy_conntrack().

Signed-off-by: Pablo Neira Ayuso <pablo@eurodev.net>
Signed-off-by: Harald Welte <laforge@netfilter.org>
Signed-off-by: David S. Miller <davem@davemloft.net>