nfq: don't warn on 'handle_packet' error

nfq: don't warn on 'handle_packet' error

NFQ can generate warnings/errors with a delay. After Suricata has
succesfully passed a verdict to the kernel, there are still things
that can go wrong for that verdict. This is then passed to the
queue through a netlink error message, which leads to nfq_handle_packet
returning an error code.

Suppress the warning. Also remove the errno/strerror use as
nfq_handle_packet does not set the errno.

Thanks to Florian Westphal.

Bug 3120.