xshared: Extend xtables_printhelp() for arptables

The function checks afinfo->family already to cover ip6tables specifics,
doing the same for arptables does not make things much worse.

This changes arptables-nft help output slightly:

* List possible negations extrapositioned, which is preferred anyway
  (arptables-nft supports both)
* List --out-interface option at lexically sorted position
* Print --wait option, it's ignored just like with iptables
* Restore default target option printing as with legacy arptables (not
  sure if arptables-nft ever did this) by explicitly loading them.

While being at it, add --set-counters short option '-c' to help output
for ip(6)tables.

This effectively removes the need for (and all users of)
xtables_global's 'print_help' callback, thus effectively reverts commit
fe83b12fc910e ("libxtables: Introduce xtables_globals print_help
callback") which broke libxtables' ABI compatibility.

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