netfilter: nf_tables: nat expression must select CONFIG_NF_NAT

This enables the netfilter NAT engine in first place, otherwise
you cannot ever select the nf_tables nat expression if iptables
is not selected.

Reported-by: Matteo Croce <technoboy85@gmail.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
index ad751fe..05eb177 100644
--- a/net/netfilter/Kconfig
+++ b/net/netfilter/Kconfig
@@ -499,7 +499,7 @@
 config NFT_NAT
 	depends on NF_TABLES
 	depends on NF_CONNTRACK
-	depends on NF_NAT
+	select NF_NAT
 	tristate "Netfilter nf_tables nat module"
 	help
 	  This option adds the "nat" expression that you can use to perform