NetworkPkg/Dhcp6Dxe: Check Media status before starting DHCP process.

This patch is to resolve the issue reported @
https://bugzilla.tianocore.org/show_bug.cgi?id=804.

Cc: Ye Ting <ting.ye@intel.com>
Cc: Fu Siyuan <siyuan.fu@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Karunakar P <karunakarp@amiindia.co.in>
Signed-off-by: Wu Jiaxin <jiaxin.wu@intel.com>
Reviewed-by: Fu Siyuan <siyuan.fu@intel.com>
(cherry picked from commit 8a5ef41ebb)

NetworkPkg/Dhcp6Dxe/Dhcp6Impl.c

@@ -1,7 +1,7 @@
 /** @file
   This EFI_DHCP6_PROTOCOL interface implementation.
 
-  Copyright (c) 2009 - 2012, Intel Corporation. All rights reserved.<BR>
+  Copyright (c) 2009 - 2017, Intel Corporation. All rights reserved.<BR>
 
   This program and the accompanying materials
   are licensed and made available under the terms and conditions of the BSD License
@@ -76,6 +76,7 @@ EfiDhcp6Start (
   EFI_TPL                      OldTpl;
   DHCP6_INSTANCE               *Instance;
   DHCP6_SERVICE                *Service;
+  BOOLEAN                      MediaPresent;
 
   if (This == NULL) {
     return EFI_INVALID_PARAMETER;
@@ -101,6 +102,17 @@ EfiDhcp6Start (
   }
 
   OldTpl           = gBS->RaiseTPL (TPL_CALLBACK);
+
+  //
+  // Check Media Satus.
+  //
+  MediaPresent = TRUE;
+  NetLibDetectMedia (Service->Controller, &MediaPresent);
+  if (!MediaPresent) {
+    Status = EFI_NO_MEDIA;
+    goto ON_ERROR;
+  }
+
   Instance->UdpSts = EFI_ALREADY_STARTED;
 
   //