iptables: libip(6)t_REJECT.man default icmp types

iptables: libip(6)t_REJECT.man default icmp types

The extension man page shows "port-unreach" and "port-unreachable" as
default icmpv6 and icomp reject-with types. Either and variations work
fine for writing rules, but they are displayed as "icmp6-port-unreachable"
and "icmp-port-unreachable". Let's make that consistent.

http://bugs.debian.org/644819

Signed-off-by: Laurence J. Lane <ljlane@debian.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>