qcacld-3.0: Don't start monitor mode if monitor interface is already up

Currently, interface status is not being checked to start monitor mode.
This is allowing to start monitor mode more than once for the same
interface. This will result in session leak during de-init.

To avoid this, start monitor mode only if the interface is not already up.

Change-Id: I118167d3a8cea52fbfa825b226b837087828f148
CRs-fixed: 2803090

core/hdd/src/wlan_hdd_main.c

@@ -2737,6 +2737,11 @@ static int __hdd_mon_open(struct net_device *dev)
 
 	hdd_enter_dev(dev);
 
+	if (test_bit(DEVICE_IFACE_OPENED, &adapter->event_flags)) {
+		hdd_debug_rl("Monitor interface is already up");
+		return 0;
+	}
+
 	ret = wlan_hdd_validate_context(hdd_ctx);
 	if (ret)
 		return ret;