NetworkPkg: Add Dpc protocol

To move Dpc.h from MdeModulePkg to NetworkPkg,
we need to introduce the Guid of protocol first.
https://bugzilla.tianocore.org/show_bug.cgi?id=1949

Cc: Siyuan Fu <siyuan.fu@intel.com>
Cc: Jiaxin Wu <jiaxin.wu@intel.com>
Signed-off-by: Shenglei Zhang <shenglei.zhang@intel.com>
Reviewed-by: Siyuan Fu <siyuan.fu@intel.com>

NetworkPkg/NetworkPkg.dec

@@ -70,6 +70,10 @@
   # Include/Guid/WifiConnectionManagerConfigHii.h
   gWifiConfigGuid               = { 0x9f94d327, 0x0b18, 0x4245, { 0x8f, 0xf2, 0x83, 0x2e, 0x30, 0xd, 0x2c, 0xef }}
 
+[Protocols]
+  ## Include/Protocol/Dpc.h
+  gEfiDpcProtocolGuid           = {0x480f8ae9, 0xc46, 0x4aa9,  { 0xbc, 0x89, 0xdb, 0x9f, 0xba, 0x61, 0x98, 0x6 }}
+
 [PcdsFixedAtBuild]
   ## The max attempt number will be created by iSCSI driver.
   # @Prompt Max attempt number.