huawei: delay processing of network-initiated disconnection

Originally developed by:
  Prathmesh Prabhu <pprabhu@chromium.org>
  Ben Chan <benchan@chromium.org>

Huawei MU736 prematurely fires a ^NDISSTAT unsolicited message upon a
network-initiated disconnection. The modem can go into a bad state if a
reconnect attempt happens before the disconnection completes. This patch works
around the issue by delaying the reporting of the disconnection.

src/mm-bearer.h

@@ -70,6 +70,7 @@ typedef enum { /*< underscore_name=mm_bearer_status >*/
 typedef enum { /*< underscore_name=mm_bearer_connection_status >*/
     MM_BEARER_CONNECTION_STATUS_UNKNOWN,
     MM_BEARER_CONNECTION_STATUS_DISCONNECTED,
+    MM_BEARER_CONNECTION_STATUS_DISCONNECTING,
     MM_BEARER_CONNECTION_STATUS_CONNECTED,
     MM_BEARER_CONNECTION_STATUS_CONNECTION_FAILED,
 } MMBearerConnectionStatus;