modem: support SIM hot swap

BaseModem
  added reprobe property.

MMDevice
  added logic to recreate the modem if it is set invalid and "to reprobe"

MMBroadbandModem
 * added initialization step for SIM hot swap:
    1. keep dedicated ports open to listen to modem's unsolicited
    2. dedicated error management in case of initialization failure due to SIM missing
 * added function to be called in order to act upon SIM insertion/removal:
    1. close dedicated ports
    2. set the modem to be reprobed
    3. disable modem
 * added SIM HOT SWAP boolean property

MMIfaceModem
 * added initialization step for SIM hot swap, if supported by the plugin
 * dedicated error management in case of initialization failure due to SIM missing

src/mm-device.c

@@ -489,8 +489,23 @@ modem_valid (MMBaseModem *modem,
              MMDevice    *self)
 {
     if (!mm_base_modem_get_valid (modem)) {
+        GDBusObjectManagerServer *object_manager = self->priv->object_manager;
+
         /* Modem no longer valid */
         mm_device_remove_modem (self);
+
+        if (mm_base_modem_get_reprobe (modem)) {
+            GError *error = NULL;
+
+            if (!mm_device_create_modem (self, object_manager, &error)) {
+                 mm_warn ("Could not recreate modem for device at '%s': %s",
+                         mm_device_get_path (self),
+                         error ? error->message : "unknown");
+                g_error_free (error);
+            } else {
+                mm_dbg ("Modem recreated for device '%s'", mm_device_get_path (self));
+            }
+        }
     } else {
         /* Modem now valid, export it, but only if we really have it around.
          * It may happen that the initialization sequence fails because the