MdePkg: Correct inconsistent function descriptions in DNS

MdePkg: Correct inconsistent function descriptions in DNS

This patch is used to correct inconsistent function descriptions
in Dns4.h and Dns6.h.

Cc: Fu Siyuan <siyuan.fu@intel.com>
Cc: Ye Ting <ting.ye@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jiaxin Wu <jiaxin.wu@intel.com>
Reviewed-by: Siyuan Fu <siyuan.fu@intel.com>
Reviewed-by: Liming Gao <liming.gao@intel.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@19780 6f19259b-4bc3-4df7-8a09-765794883524