NetworkPkg: Replace UnicodeStrToAsciiStr/AsciiStrToUnicodeStr

NetworkPkg: Replace UnicodeStrToAsciiStr/AsciiStrToUnicodeStr

It is the follow up of 3ab41b7a325ca11a12b42f5ad1661c4b6791cb49
to replace UnicodeStrToAsciiStr/AsciiStrToUnicodeStr with
UnicodeStrToAsciiStrS/AsciiStrToUnicodeStrS.

Cc: Jiewen Yao <jiewen.yao@intel.com>
Cc: Siyuan Fu <siyuan.fu@intel.com>
Cc: Jiaxin Wu <jiaxin.wu@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>
Reviewed-by: Jiaxin Wu <jiaxin.wu@intel.com>
Reviewed-by: Siyuan Fu <siyuan.fu@intel.com>