qcom-soc: require udev tag for ports

Since the 'wwan' subsystem addition to the qcom-soc plugin, the rules
to say a modem is handled by this plugin are too broad, and the plugin
attempts to support any kind of device exposed by the WWAN subsystem,
not just those from Qualcomm SoCs.

Update the plugin to require a new ID_MM_QCOM_SOC udev tag that is set
in the plugin udev rules, given that these rules already check for the
expected SoC drivers (bam-dmux, ipa, qcom-q6v5-mss).

plugins/qcom-soc/mm-plugin-qcom-soc.c

@@ -68,6 +68,10 @@ G_MODULE_EXPORT MMPlugin *
 mm_plugin_create (void)
 {
     static const gchar *subsystems[] = { "wwan", "rpmsg", "net", "qrtr", NULL };
+    static const gchar *udev_tags[] = {
+        "ID_MM_QCOM_SOC",
+        NULL
+    };
 
     return MM_PLUGIN (
         g_object_new (MM_TYPE_PLUGIN_QCOM_SOC,
@@ -75,6 +79,7 @@ mm_plugin_create (void)
                       MM_PLUGIN_ALLOWED_SUBSYSTEMS, subsystems,
                       MM_PLUGIN_ALLOWED_AT,         TRUE,
                       MM_PLUGIN_ALLOWED_QMI,        TRUE,
+                      MM_PLUGIN_ALLOWED_UDEV_TAGS,  udev_tags,
                       NULL));
 }