kernel: add menuconfig entry for kernel CONFIG_CGROUP_NET_CLASSID

It was removed from target defaults though it didn't exist in the
build-systems kernel configuration options. Add it there.

Fixes: d1a8217d87 ("kernel: clean-up build-configurable kernel config symbols")
Signed-off-by: Daniel Golle <[email protected]>

config/Config-kernel.in

@@ -795,6 +795,10 @@ if KERNEL_CGROUPS
 		bool "legacy Control Group Classifier"
 		default n
 
+	config KERNEL_CGROUP_NET_CLASSID
+		bool "legacy Network classid cgroup"
+		default n
+
 	config KERNEL_CGROUP_NET_PRIO
 		bool "legacy Network priority cgroup"
 		default n