scripts: check_site_lib: need_table() now merges all keys before calling subcheck(...)

This also introduces an api change to the subcheck()!

Before:
-> subcheck(key, value, conf_name)

After:
-> subcheck(key, conf_name)

The idea is, that it's hard to submit a value, which should be then checked
again. It's wouldn't be clear (after merging) from which config the value
is, and so an helpful error message would be impossible.

package/gluon-autoupdater/check_site.lua

@@ -1,6 +1,6 @@
 need_string(in_site('autoupdater.branch'))
 
-local function check_branch(k, _, conf_name)
+local function check_branch(k, conf_name)
    assert_uci_name(k, conf_name)
 
    local prefix = string.format('autoupdater.branches[%q].', k)

package/gluon-core/check_site.lua

@@ -5,7 +5,7 @@ need_string_match(in_site('site_seed'), '^' .. ('%x'):rep(64) .. '$')
 if need_table('opkg', nil, false) then
 	need_string('opkg.lede', false)
 
-	function check_repo(k, _, conf_name)
+	function check_repo(k, conf_name)
 		-- this is not actually a uci name, but using the same naming rules here is fine
 		assert_uci_name(k, conf_name)
 

package/gluon-mesh-vpn-fastd/check_site.lua

@@ -5,7 +5,7 @@ need_boolean(in_site('mesh_vpn.fastd.configurable'), false)
 need_one_of(in_site('mesh_vpn.fastd.syslog_level'), {'error', 'warn', 'info', 'verbose', 'debug', 'debug2'}, false)
 
 local function check_peer(prefix)
-	return function(k, _, conf_name)
+	return function(k, conf_name)
 		assert_uci_name(k, conf_name)
 
 		local table = string.format('%s[%q].', prefix, k)
@@ -16,7 +16,7 @@ local function check_peer(prefix)
 end
 
 local function check_group(prefix)
-	return function(k, _, conf_name)
+	return function(k, conf_name)
 		assert_uci_name(k, conf_name)
 
 		local table = string.format('%s[%q].', prefix, k)