iface-modem: allow changing the State from outside the interface

Some states need to be set from outside the scope of the Modem interface, like
Registration-related ones (REGISTERED, SEARCHING, ...) or Connection-related
ones (CONNECTED, ...).

src/mm-iface-modem.h

@@ -296,4 +296,9 @@ guint mm_iface_modem_signal_quality_check_finish (MMIfaceModem *self,
                                                   gboolean *recent,
                                                   GError **error);
 
+/* Allow reporting new modem state */
+void mm_iface_modem_update_state (MMIfaceModem *self,
+                                  MMModemState new_state,
+                                  MMModemStateReason reason);
+
 #endif /* MM_IFACE_MODEM_H */