netfilter: nf_nat: don't check if the tuple is unique when there isn't any other...

The tuple got from unique_tuple() doesn't need to be really unique, so the
check for the unique tuple isn't necessary, when there isn't any other
choice. Eliminating the unnecessary nf_nat_used_tuple() can save some CPU
cycles too.

Signed-off-by: Changli Gao <xiaosuo@gmail.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>

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

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

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