libxt_conntrack: improve error message on parsing violation

libxt_conntrack: improve error message on parsing violation

Tom Eastep noted:

$ iptables -A foo -m conntrack --ctorigdstport 22
iptables v1.4.12: conntrack rev 2 does not support port ranges
Try `iptables -h' or 'iptables --help' for more information.

Commit v1.4.12-41-g1ad6407 takes care of the actual cause of the bug,
but let's include Tom's patch nevertheless for the better error
message in case one actually does specify a range with rev 2.

References: http://marc.info/?l=netfilter-devel&m=131370592105298&w=2
Signed-off-by: Jan Engelhardt <jengelh@medozas.de>