iptables: always print mask in iptables-save

iptables: always print mask in iptables-save

iptables prints the mask as a prefix length if it is valid;
This patch makes iptables-save do the same.

Also, iptables-save will always print "/32" in the "-s addr/32"
case now. This reduces the amount of code external parsing scripts
need to provide to properly parse iptables-save output.

ip6tables-save already does the right thing, so no change there.

Signed-off-by: Jan Engelhardt <jengelh@computergmbh.de>