MdeModulePkg/Ip4Dxe: Sync the direct route entry setting.

v2: use "IP & Netmask" directly instead of defining an additional variable.

This patch is to sync the direct route entry setting in both the default
and Instance route table {Subnet, Mask, NextHope} (
https://bugzilla.tianocore.org/show_bug.cgi?id=1143).

Cc: Ye Ting <ting.ye@intel.com>
Cc: Fu Siyuan <siyuan.fu@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Wu Jiaxin <jiaxin.wu@intel.com>
Reviewed-by: Ye Ting <ting.ye@intel.com>
Reviewed-by: Fu Siyuan <siyuan.fu@intel.com>

MdeModulePkg/Universal/Network/Ip4Dxe/Ip4Config2Impl.c

@@ -559,13 +559,6 @@ Ip4Config2SetDefaultAddr (
     }
   }
 
-  Ip4AddRoute (
-    IpSb->DefaultRouteTable,
-    StationAddress,
-    SubnetMask,
-    IP4_ALLZERO_ADDRESS
-    );
-
   //
   // Add a route for the connected network.
   //