netfilter: nfnetlink_queue: fix compilation with NF_CONNTRACK disabled

In "9cb0176 netfilter: add glue code to integrate nfnetlink_queue and ctnetlink"
the compilation with NF_CONNTRACK disabled is broken. This patch fixes this
issue.

I have moved the conntrack part into nfnetlink_queue_ct.c to avoid
peppering the entire nfnetlink_queue.c code with ifdefs.

I also needed to rename nfnetlink_queue.c to nfnetlink_queue_pkt.c
to update the net/netfilter/Makefile to support conditional compilation
of the conntrack integration.

This patch also adds CONFIG_NETFILTER_QUEUE_CT in case you want to explicitly
disable the integration between nf_conntrack and nfnetlink_queue.

Reported-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
diff --git a/net/netfilter/Kconfig b/net/netfilter/Kconfig
index f1a52ba..c19b214 100644
--- a/net/netfilter/Kconfig
+++ b/net/netfilter/Kconfig
@@ -340,6 +340,7 @@
 	select NETFILTER_NETLINK
 	depends on NF_CT_NETLINK
 	depends on NETFILTER_NETLINK_QUEUE
+	depends on NETFILTER_NETLINK_QUEUE_CT
 	depends on NETFILTER_ADVANCED
 	help
 	  This option enables the user-space connection tracking helpers
@@ -347,6 +348,14 @@
 
 	  If unsure, say `N'.
 
+config NETFILTER_NETLINK_QUEUE_CT
+        bool "NFQUEUE integration with Connection Tracking"
+        default n
+        depends on NETFILTER_NETLINK_QUEUE
+	help
+	  If this option is enabled, NFQUEUE can include Connection Tracking
+	  information together with the packet is the enqueued via NFNETLINK.
+
 endif # NF_CONNTRACK
 
 # transparent proxy support