gluon-core: provide migration for preserve_channels

The preserve_channels configuration option was moved to the gluon UCI
package without adding a proper migration.

Signed-off-by: David Bauer <mail@david-bauer.net>

package/gluon-core/luasrc/lib/gluon/upgrade/190-preserve-wireless-channels

+#!/usr/bin/lua
+
+local wireless = require 'gluon.wireless'
+local uci = require('simple-uci').cursor()
+
+local preserve_channels = wireless.preserve_channels(uci)
+
+-- Migrate preserve channels from pre-2022.01
+local core_wireless = uci:get_first('gluon-core', 'wireless')
+if core_wireless ~= nil then
+	local preserve_legacy = uci:get_bool('gluon-core', core_wireless, 'preserve_channels')
+	if preserve_legacy then
+		preserve_channels = true
+	end
+
+	uci:delete('gluon-core', core_wireless)
+	uci:save('gluon-core')
+end
+
+uci:section('gluon', 'wireless', 'wireless', {
+	preserve_channels = preserve_channels or false,
+})
+uci:save('gluon')