libipt_[SD]NAT: avoid false error about multiple destinations specified

iptables-restore v1.4.10: DNAT: Multiple --to-destination not supported

xtables_option_parse sets cb->xflags already, so that it cannot be
directly used to test whether an option is being used for the second
time. Thus use a private option/flag (X_TO_DEST/SRC) that is not under
the control of xtables_option_parse.

Signed-off-by: Jan Engelhardt <jengelh@medozas.de>
2 files changed