netfilter: ipset: Consistent userspace testing with nomatch flag

The "nomatch" commandline flag should invert the matching at testing,
similarly to the --return-nomatch flag of the "set" match of iptables.
Until now it worked with the elements with "nomatch" flag only. From
now on it works with elements without the flag too, i.e:

 # ipset n test hash:net
 # ipset a test 10.0.0.0/24 nomatch
 # ipset t test 10.0.0.1
 10.0.0.1 is NOT in set test.
 # ipset t test 10.0.0.1 nomatch
 10.0.0.1 is in set test.

 # ipset a test 192.168.0.0/24
 # ipset t test 192.168.0.1
 192.168.0.1 is in set test.
 # ipset t test 192.168.0.1 nomatch
 192.168.0.1 is NOT in set test.

 Before the patch the results were

 ...
 # ipset t test 192.168.0.1
 192.168.0.1 is in set test.
 # ipset t test 192.168.0.1 nomatch
 192.168.0.1 is in set test.

Signed-off-by: Jozsef Kadlecsik <kadlec@blackhole.kfki.hu>