netfilter: ipset: support range for IPv4 at adding/deleting elements for hash:*net* types

The range internally is converted to the network(s) equal to the range.
Example:

	# ipset new test hash:net
	# ipset add test 10.2.0.0-10.2.1.12
	# ipset list test
	Name: test
	Type: hash:net
	Header: family inet hashsize 1024 maxelem 65536
	Size in memory: 16888
	References: 0
	Members:
	10.2.1.12
	10.2.1.0/29
	10.2.0.0/24
	10.2.1.8/30

Signed-off-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>
Signed-off-by: Patrick McHardy <kaber@trash.net>