gluon-web-mesh-vpn-fastd: clarify config of default crypto method (#1502)

docs/features/vpn.rst

@@ -32,8 +32,9 @@ increase throughput, although in practice the gain is minimal.
 
 **Site configuration:**
 
-1) Install ``gluon-web-mesh-vpn-fastd`` in ``site.mk``
+1) Add the feature ``web-mesh-vpn-fastd`` in ``site.mk``
 2) Set ``mesh_vpn.fastd.configurable = true`` in ``site.conf``
+3) Optionally add ``null`` to the ``mesh_vpn.fastd.methods`` table if you want "Performance mode" as default (not recommended)
 
 **Gateway configuration:**
 
@@ -54,4 +55,3 @@ socket can be interrogated, after installing for example `socat`.
        opkg update
        opkg install socat
        socat - UNIX-CONNECT:/var/run/fastd.mesh_vpn.socket
-

package/gluon-web-mesh-vpn-fastd/luasrc/lib/gluon/config-mode/model/admin/mesh_vpn_fastd.lua

@@ -11,6 +11,7 @@ mode.template = "mesh-vpn-fastd"
 
 local methods = uci:get('fastd', 'mesh_vpn', 'method')
 if util.contains(methods, 'null') then
+	-- performance mode will only be used as default, if it is present in site.mesh_vpn.fastd.methods
 	mode.default = 'performance'
 else
 	mode.default = 'security'
@@ -19,6 +20,8 @@ end
 function mode:write(data)
 	local site = require 'gluon.site'
 
+	-- methods will be recreated and filled with the original values from site.mesh_vpn.fastd.methods
+	-- if performance mode was selected, and the method 'null' was not present in the original table, it will be added
 	local methods = {}
 	if data == 'performance' then
 		table.insert(methods, 'null')