selftests/net: replace obsolete NFT_CHAIN configuration

Replace old parameters with global NFT_NAT from commit db8ab388
("netfilter: nf_tables: merge ipv4 and ipv6 nat chain types")
Signed-off-by: Fabian Frederick <fabf@skynet.be>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

tools/testing/selftests/net/config

@@ -24,8 +24,7 @@ CONFIG_IP_NF_NAT=m
 CONFIG_NF_TABLES=m
 CONFIG_NF_TABLES_IPV6=y
 CONFIG_NF_TABLES_IPV4=y
-CONFIG_NFT_CHAIN_NAT_IPV6=m
-CONFIG_NFT_CHAIN_NAT_IPV4=m
+CONFIG_NFT_NAT=m
 CONFIG_NET_SCH_FQ=m
 CONFIG_NET_SCH_ETF=m
 CONFIG_NET_SCH_NETEM=y