NetworkPkg: Add IPv6 DUID configuration support using platform PCD.

The code today always uses DUID-UUID unless there is an error in reading the UUID, 
which results in falling through to DUID-LLT. This change allows the platform to
 control the DUID method (DUID-UUID or DUID-LLT) using a platform dynamic PCD.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Samer El-Haj-Mahmoud <elhaj@hp.com>
Reviewed-by: Fu Siyuan <siyuan.fu@intel.com>

git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@17751 6f19259b-4bc3-4df7-8a09-765794883524

NetworkPkg/Dhcp6Dxe/Dhcp6Dxe.inf

@@ -4,6 +4,7 @@
 #  This driver produces EFI DHCPv6 Protocol which is used to get IPv6 addresses
 #  and other configuration parameters from DHCPv6 servers.
 #
+#  (C) Copyright 2015 Hewlett-Packard Development Company, L.P.<BR>
 #  Copyright (c) 2009 - 2014, Intel Corporation. All rights reserved.<BR>
 #
 #  This program and the accompanying materials
@@ -51,7 +52,7 @@
 [Packages]
   MdePkg/MdePkg.dec
   MdeModulePkg/MdeModulePkg.dec
-
+  NetworkPkg/NetworkPkg.dec
 
 [LibraryClasses]
   UefiLib
@@ -73,5 +74,9 @@
   gEfiDhcp6ProtocolGuid                              ## BY_START
   gEfiIp6ConfigProtocolGuid                          ## TO_START
 
+ 
+[Pcd]
+  gEfiNetworkPkgTokenSpaceGuid.PcdDhcp6UidType
+
 [UserExtensions.TianoCore."ExtraFiles"]
   Dhcp6DxeExtra.uni