selftests: netfilter: fix config fragment CONFIG_NF_TABLES_INET

In selftests the config fragment for netfilter was added as
NF_TABLES_INET=y and this patch correct it as CONFIG_NF_TABLES_INET=y
Signed-off-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Acked-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

tools/testing/selftests/netfilter/config

 CONFIG_NET_NS=y
-NF_TABLES_INET=y
+CONFIG_NF_TABLES_INET=y