Add user namespace check to check-chonfig.sh

Signed-off-by: Lei Jitang <leijitang@huawei.com>

contrib/check-config.sh

@@ -180,6 +180,9 @@ check_flags "${flags[@]}"
 echo
 
 echo 'Optional Features:'
+{
+	check_flags USER_NS
+}
 {
 	check_flags MEMCG_KMEM MEMCG_SWAP MEMCG_SWAP_ENABLED
 	if  is_set MEMCG_SWAP && ! is_set MEMCG_SWAP_ENABLED; then
@@ -240,6 +243,3 @@ echo '- Storage Drivers:'
 } | sed 's/^/  /'
 echo
 
-#echo 'Potential Future Features:'
-#check_flags USER_NS
-#echo