iproute2: Fix building xt module against xtables version 6

iproute2: Fix building xt module against xtables version 6

iptables/xtables apparently changed API again.... Now you need to pass
and extra parameter (orig_opts) which was not needed before.

Sprinkle some lovely pre-processor magic to be compatible with both older
and new versions. In the beginning of times XTABLES_VERSION_CODE didn't
exist. Then it was (0x10000 * major + 0x100 * minor + patch) when it was
first introduced (according to git), but now it's at 6...
Don't know what official iptables releases has defined it to over time.
Lets just hope none of the older versions with is has the define
higher then 6 is still around.... so only the "current" versioning
scheme is supported.... lets see how long this lasts now.

For the API change in xtables, see:
http://git.netfilter.org/cgi-bin/gitweb.cgi?p=iptables.git;a=commitdiff;h=600f38db82548a683775fd89b6e136673e924097

Signed-off-by: Andreas Henriksson <andreas@fatal.se>