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/Dhcp4Dxe/Dhcp4Io.c

@@ -78,7 +78,7 @@ EFI_STATUS
 DhcpCallUser (
   IN  DHCP_SERVICE          *DhcpSb,
   IN  EFI_DHCP4_EVENT       Event,
-  IN  EFI_DHCP4_PACKET      *Packet,      OPTIONAL
+  IN  EFI_DHCP4_PACKET      *Packet       OPTIONAL,
   OUT EFI_DHCP4_PACKET      **NewPacket   OPTIONAL
   )
 {