Unbreak xtables-translate

Unbreak xtables-translate

Fixed commit broke xtables-translate which still relied upon do_parse()
to properly initialize the passed iptables_command_state reference. To
allow for callers to preset fields, this doesn't happen anymore so
do_command_xlate() has to initialize itself. Otherwise garbage from
stack is read leading to segfaults and program aborts.

Although init_cs callback is used by arptables only and
arptables-translate has not been implemented, do call it if set just to
avoid future issues.

Fixes: cfdda18044d81 ("nft-shared: Introduce init_cs family ops callback")
Signed-off-by: Phil Sutter <phil@nwl.cc>
Tested-by: Pablo Neira Ayuso <pablo@netfilter.org>