Add IPFW_RULE_JUSTOPTS flag, that is used by ipfw(8) to mark rule,
that was added using "new rule format". And then, when the kernel
returns rule with this flag, ipfw(8) can correctly show it.

Reported by:	lev
Sponsored by:	Yandex LLC
Differential Revision:	https://reviews.freebsd.org/D17373