[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 <toralf.foerster@gmx.de>.
Signed-off-by: NPatrick McHardy <kaber@trash.net>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/netfilter/Kconfig

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