gsm: fix up CID signed/unsigned confusion

-1 = no APN set, so use modem default.  We'll have to fix a few
more things up for modems like hso/mbm that don't use ATDT and
require CIDs, but this gets us halfway there for other devices.

plugins/mm-modem-hso.c

@@ -431,7 +431,7 @@ unsolicited_disable_done (MMModem *modem,
     }
 
     /* Otherwise, kill any existing connection */
-    if (mm_generic_gsm_get_cid (MM_GENERIC_GSM (modem)) >= 0)
+    if (hso_get_cid (MM_MODEM_HSO (modem)) >= 0)
         hso_call_control (MM_MODEM_HSO (modem), FALSE, TRUE, disable_done, info);
     else
         disable_done (modem, NULL, info);

plugins/mm-modem-mbm.c

@@ -728,18 +728,15 @@ mbm_auth_done (MMSerialPort *port,
     MMCallbackInfo *info = (MMCallbackInfo *) user_data;
     MMGenericGsm *modem = MM_GENERIC_GSM (info->modem);
     char *command;
-    guint32 cid;
 
     if (error) {
         mm_generic_gsm_connect_complete (modem, error, info);
         return;
     }
 
-    cid = mm_generic_gsm_get_cid (modem);
-
     mm_at_serial_port_queue_command (MM_AT_SERIAL_PORT (port), "AT*E2NAP=1", 3, NULL, NULL);
 
-    command = g_strdup_printf ("AT*ENAP=1,%d", cid);
+    command = g_strdup_printf ("AT*ENAP=1,%d", mm_generic_gsm_get_cid (modem));
     mm_at_serial_port_queue_command (MM_AT_SERIAL_PORT (port), command, 3, enap_done, user_data);
     g_free (command);
 }

src/mm-generic-gsm.c

@@ -2695,7 +2695,7 @@ connect (MMModem *modem,
     MMGenericGsmPrivate *priv = MM_GENERIC_GSM_GET_PRIVATE (modem);
     MMCallbackInfo *info;
     char *command;
-    guint32 cid = mm_generic_gsm_get_cid (MM_GENERIC_GSM (modem));
+    gint cid = mm_generic_gsm_get_cid (MM_GENERIC_GSM (modem));
 
     info = mm_callback_info_new (modem, callback, user_data);