fix code style issue and add function header

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@6570 6f19259b-4bc3-4df7-8a09-765794883524

MdeModulePkg/Universal/Network/MnpDxe/MnpIo.c

@@ -124,8 +124,6 @@ MnpIsValidTxToken (
   @param  PktLen                Pointer to a UINT32 variable used to record the
                                 packet's length.
 
-  @return None.
-
 **/
 VOID
 MnpBuildTxPacket (
@@ -434,8 +432,6 @@ MnpDeliverPacket (
   @param  Event                 The event this notify function registered to.
   @param  Context               Pointer to the context data registerd to the Event.
 
-  @return None.
-
 **/
 VOID
 EFIAPI
@@ -1007,9 +1003,7 @@ EXIT:
   @param  Event                 The event this notify function registered to.
   @param  Context               Pointer to the context data registered to the
                                 event.
-
-  @return None.
-
+   
 **/
 VOID
 EFIAPI