netfilter: fix IP_VS dependencies

When NF_CONNTRACK is enabled, IP_VS uses conntrack symbols.
Therefore IP_VS can't be linked statically when conntrack
is built modular.
Reported-by: Justin P. Mattock <justinmattock@gmail.com>
Tested-by: Justin P. Mattock <justinmattock@gmail.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/netfilter/ipvs/Kconfig

@@ -4,6 +4,7 @@
 menuconfig IP_VS
 	tristate "IP virtual server support"
 	depends on NET && INET && NETFILTER
+	depends on (NF_CONNTRACK || NF_CONNTRACK=n)
 	---help---
 	  IP Virtual Server support will let you build a high-performance
 	  virtual server based on cluster of two or more real servers. This