Exceptions support added to hash:*net* types

Exceptions support added to hash:*net* types

The "nomatch" keyword and option is added to the hash:*net* types,
by which one can add exception entries to sets. Example:

	ipset create test hash:net
	ipset add test 192.168.0/24
	ipset add test 192.168.0/30 nomatch

In this case the IP addresses from 192.168.0/24 except 192.168.0/30
match the elements of the set.