iface-modem: let different SIM object creation implementations

We let objects implementing the Modem interface to provide their own SIM
creation method. This allows plugins to subclass MMSim themselves.

src/mm-iface-modem.h

@@ -22,6 +22,7 @@
 #include "mm-charsets.h"
 #include "mm-at-serial-port.h"
 #include "mm-bearer.h"
+#include "mm-sim.h"
 
 #define MM_TYPE_IFACE_MODEM            (mm_iface_modem_get_type ())
 #define MM_IFACE_MODEM(obj)            (G_TYPE_CHECK_INSTANCE_CAST ((obj), MM_TYPE_IFACE_MODEM, MMIfaceModem))
@@ -253,6 +254,14 @@ struct _MMIfaceModem {
                                          GAsyncResult *res,
                                          GError **error);
 
+    /* Create SIM */
+    void (*create_sim) (MMIfaceModem *self,
+                        GAsyncReadyCallback callback,
+                        gpointer user_data);
+    MMSim * (*create_sim_finish) (MMIfaceModem *self,
+                                  GAsyncResult *res,
+                                  GError **error);
+
     /* Create bearer */
     void (*create_bearer) (MMIfaceModem *self,
                            MMCommonBearerProperties *properties,