[NETFILTER]: nf_conntrack: properly use RCU for nf_conntrack_destroyed callback

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --cc net/ipv4/netfilter/nf_nat_core.c
Simple merge

diff --cc net/netfilter/nf_conntrack_core.c
Simple merge