networkAgent: Pick up VPN service dir from pkg-config

It turns out that NetworkManager does export the directory as pkg-config
variable after all, so use that instead of building the path ourselves
from the prefix.

https://bugzilla.gnome.org/show_bug.cgi?id=789811

js/misc/config.js.in

@@ -14,6 +14,6 @@ var GETTEXT_PACKAGE = '@GETTEXT_PACKAGE@';
 var LOCALEDIR = '@datadir@/locale';
 /* other standard directories */
 var LIBEXECDIR = '@libexecdir@';
-var NMPREFIXDIR = '@nmprefixdir@';
+var VPNDIR = '@vpndir@';
 /* g-i package versions */
 var LIBMUTTER_API_VERSION = '@LIBMUTTER_API_VERSION@'

js/misc/meson.build

@@ -7,7 +7,7 @@ jsconf.set10('HAVE_BLUETOOTH', bt_dep.found())
 jsconf.set10('HAVE_NETWORKMANAGER', have_networkmanager)
 jsconf.set('datadir', datadir)
 jsconf.set('libexecdir', libexecdir)
-jsconf.set('nmprefixdir', nm_prefix)
+jsconf.set('vpndir', vpndir)
 
 config_js = configure_file(
   input: 'config.js.in',

js/ui/components/networkAgent.js

@@ -594,7 +594,7 @@ var NetworkAgent = new Lang.Class({
         this._vpnRequests = { };
         this._notifications = { };
 
-        this._pluginDir = Gio.file_new_for_path(GLib.build_filenamev([Config.NMPREFIXDIR, 'lib/NetworkManager/VPN']));
+        this._pluginDir = Gio.file_new_for_path(Config.VPNDIR);
         try {
             let monitor = this._pluginDir.monitor(Gio.FileMonitorFlags.NONE, null);
             monitor.connect('changed', () => { this._vpnCacheBuilt = false; });