netfilter: fix missing dependencies for NETFILTER_XT_MATCH_CONNLABEL

It was possible to set NF_CONNTRACK=n and NF_CONNTRACK_LABELS=y via
NETFILTER_XT_MATCH_CONNLABEL=y.

warning: (NETFILTER_XT_MATCH_CONNLABEL) selects NF_CONNTRACK_LABELS which has
unmet direct dependencies (NET && INET && NETFILTER && NF_CONNTRACK)

Reported-by: Randy Dunlap <[e-mail]>
Signed-off-by: Florian Westphal <[e-mail]>
Acked-by: Randy Dunlap <[e-mail]>
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

net/netfilter/Kconfig

···
 config NETFILTER_XT_MATCH_CONNLABEL
 	tristate '"connlabel" match support'
 	select NF_CONNTRACK_LABELS
+	depends on NF_CONNTRACK
 	depends on NETFILTER_ADVANCED
 	---help---
 	  This match allows you to test and assign userspace-defined labels names