motmdm: HACK: wait before opening next tty device

It seems that modem is not fast enough to respond in time if multiple
channel open requests are done in parallel. This result in only DLC 1 being
functional if ofono is restarted.

Fix that by delaying each consecutive open

Signed-off-by: Ivaylo Dimitrov <ivo.g.dimitrov.75@gmail.com>

plugins/motmdm.c

@@ -401,6 +401,11 @@ static int motmdm_open_dlc_devices(struct ofono_modem *modem)
 			break;
 		}
 
+		/* If we open in a row, all channels but 1 time out on SABM(P)
+		 * request, effectively remaining closed. Give modem a chance to
+		 * catch up.
+		 */
+		sleep(1);
 		found++;
 	}