extensions: libipt_icmp: Fix confusion between 255/255 and any

extensions: libipt_icmp: Fix confusion between 255/255 and any

Per definition, ICMP type "any" is type 255 and the full range of codes
(0-255). Save callback though ignored the actual code values, printing
"any" for every type 255 match. This at least confuses users as they
can't find their rule added as '--icmp-type 255/255' anymore.

It is not entirely clear what the fixed commit was trying to establish,
but the save output is certainly not correct (especially since print
callback gets things right).

Reported-by: Amelia Downs <adowns@vmware.com>
Closes: https://bugzilla.netfilter.org/show_bug.cgi?id=1600
Fixes: fc9237da4e845 ("Fix '-p icmp -m icmp' issue (Closes: #37)")
Signed-off-by: Phil Sutter <phil@nwl.cc>