NetworkPkg: Change OPTIONAL keyword usage style

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=3760

Update all use of ', OPTIONAL' to ' OPTIONAL,' for function params.

Cc: Andrew Fish <afish@apple.com>
Cc: Leif Lindholm <leif@nuviainc.com>
Cc: Michael Kubacki <michael.kubacki@microsoft.com>
Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
Reviewed-by: Maciej Rabeda <maciej.rabeda@linux.intel.com>

NetworkPkg/SnpDxe/Transmit.c

@@ -274,8 +274,8 @@ SnpUndi32Transmit (
   IN UINTN                       HeaderSize,
   IN UINTN                       BufferSize,
   IN VOID                        *Buffer,
-  IN EFI_MAC_ADDRESS             *SrcAddr,  OPTIONAL
-  IN EFI_MAC_ADDRESS             *DestAddr, OPTIONAL
+  IN EFI_MAC_ADDRESS             *SrcAddr   OPTIONAL,
+  IN EFI_MAC_ADDRESS             *DestAddr  OPTIONAL,
   IN UINT16                      *Protocol  OPTIONAL
   )
 {