plugin: allow to explicitly ignore any kind of port via udev

The new 'ID_MM_PORT_IGNORE' tag will tell ModemManager to fully avoid using a
given port.

Note that it is key to not only flag the port probe as ignored, but also to
fully ignore the ports in e.g. mm_port_probe_list_has_qmi_port() as those
methods will be used to decide which kind of modem object to create. We don't
want to create a QMI-based modem which may have all QMI ports blacklisted.

src/mm-plugin.c

@@ -865,6 +865,19 @@ mm_plugin_create_modem (MMPlugin  *self,
                                            "unsupported subsystem: '%s'",
                                            mm_port_probe_get_port_subsys (probe));
             }
+            /* Ports that are explicitly blacklisted will be grabbed as ignored */
+            else if (mm_port_probe_is_ignored (probe)) {
+                mm_dbg ("(%s/%s): port is blacklisted",
+                        mm_port_probe_get_port_subsys (probe),
+                        mm_port_probe_get_port_name (probe));
+                grabbed = mm_base_modem_grab_port (modem,
+                                                   mm_port_probe_get_port_subsys (probe),
+                                                   mm_port_probe_get_port_name (probe),
+                                                   mm_port_probe_get_parent_path (probe),
+                                                   MM_PORT_TYPE_IGNORED,
+                                                   MM_PORT_SERIAL_AT_FLAG_NONE,
+                                                   &inner_error);
+            }
 #if !defined WITH_QMI
             else if (mm_port_probe_get_port_type (probe) == MM_PORT_TYPE_NET &&
                      g_str_equal (mm_device_utils_get_port_driver (mm_port_probe_peek_port (probe)),