netfilter: x_tables: remove pr_info where possible

remove several pr_info messages that cannot be triggered with iptables,
the check is only to ensure input is sane.

iptables(8) already prints error messages in these cases.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>