networkAgent: Fix fallout from libnm port

While the libnm-glib version of the function returns a GByteArray*
that gjs can directly cast to the required gutf8*, the libnm function
returns GBytes* from which we need to explicitly fetch the data.

https://gitlab.gnome.org/GNOME/gnome-shell/issues/136

js/ui/components/networkAgent.js

@@ -660,7 +660,7 @@ var NetworkAgent = new Lang.Class({
         switch (connectionType) {
         case '802-11-wireless':
             let wirelessSetting = connection.get_setting_wireless();
-            let ssid = NM.utils_ssid_to_utf8(wirelessSetting.get_ssid());
+            let ssid = NM.utils_ssid_to_utf8(wirelessSetting.get_ssid().get_data());
             title = _("Authentication required by wireless network");
             body = _("Passwords or encryption keys are required to access the wireless network “%s”.").format(ssid);
             break;