Update network stack code to use StrnCpy instead of StrCpy.

Update network stack code to use StrnCpy instead of StrCpy.
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Fu, Siyuan <siyuan.fu@intel.com>
Reviewed-By: Dong, Eric <eric.dong@intel.com>
Reviewed-by: Wu, Jiaxin <jiaxin.wu@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@15773 6f19259b-4bc3-4df7-8a09-765794883524