[NETFILTER]: nf_nat: remove unused argument of function allocating binding

nf_nat_rule_find, alloc_null_binding and alloc_null_binding_confirmed
do not use the argument 'info', which is actually ct->nat.info.
If they are necessary to access it again, we can use the argument 'ct'
instead.

Signed-off-by: Yasuyuki Kozakai <yasuyuki.kozakai@toshiba.co.jp>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>