netfilter: ipset: use nla_strcmp for IPSET_ATTR_NAME attr

netfilter: ipset: use nla_strcmp for IPSET_ATTR_NAME attr

IPSET_ATTR_NAME and IPSET_ATTR_NAMEREF are of NLA_STRING type, they
cannot be treated like a c-string.

They either have to be switched to NLA_NUL_STRING, or the compare
operations need to use the nla functions.

Fixes: f830837f0eed ("netfilter: ipset: list:set set type support")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>