xshared: Merge invflags handling code

Join invflags handling between iptables, ip6tables, xtables and
arptables. Ebtables still has its own code which differs quite a bit.

In order to use a shared set_option() routine, iptables and ip6tables
need to provide a local 'invflags' variable which is 16bits wide.

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