[NETFILTER]: Fix INET=n linking error

Building with INET=n results in

WARNING: "ip_route_output_key" [net/netfilter/nf_conntrack_h323.ko] undefined!

The entire code in net/netfilter is only used for IPv4/IPv6 currently, so
let it depend on INET.

Noticed by Toralf Förster <[e-mail]>.

Signed-off-by: Patrick McHardy <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/netfilter/Kconfig

···
 menu "Core Netfilter Configuration"
-	depends on NET && NETFILTER
+	depends on NET && INET && NETFILTER
 
 config NETFILTER_NETLINK
        tristate "Netfilter netlink interface"