libip6t_frag: match any frag id by default

libip6t_frag: match any frag id by default

If no --fragid option is given, the frag extension only matches
fragments with a zero-valued "Identification" field. This behavior
deviates from what other extensions do (they match all values in this
case) and is unexpected, and therefore changed by this patch.

Additionally, --fragid 0:4294967295 leads to no output on `iptables
-S` because part of the code thinks that this would be the default,
when it is not.

So, default to match all frag values, such that iptables -S not
outputting anything also becomes correct.

Signed-off-by: Michal Kubecek <mkubecek@suse.cz>
Signed-off-by: Jan Engelhardt <jengelh@inai.de>