MdeModulePkg: Did some code enhancement for DxeIpIoLib.

* In DxeIpIo, there are several places use ASSERT() to check input
  parameters without and descriptions or error handling. This patch
  fixed this issue.
* Fixed some incorrect descriptions in code commence.
* Remove unneeded Exit tag in function IpIoOpen and IpIoConfigIp.
* Add EFIAPI tag for function IpIoRefreshNeighbor.

Cc: Jiaxin Wu <jiaxin.wu@intel.com>
Cc: Ye Ting <ting.ye@intel.com>
Cc: Fu Siyuan <siyuan.fu@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Wang Fan <fan.wang@intel.com>
Reviewed-by: Jiaxin Wu <jiaxin.wu@intel.com>
Reviewed-by: Fu Siyuan <siyuan.fu@intel.com>