xshared: Share save_rule_details() with legacy

xshared: Share save_rule_details() with legacy

The function combines printing of input and output interfaces and
protocol parameter, all being IP family independent. Extend the function
to print fragment option ('-f'), too if requested. While being at it,
drop unused iptables_command_state parameter and reorder the remaining
ones a bit.

Signed-off-by: Phil Sutter <phil@nwl.cc>