ShellPkg: update ping6 to use timer service instead of timer arch protocol .

ShellPkg: update ping6 to use timer service instead of timer arch protocol .

This patch update the shell ping command to use timer service to calculate the
RTT time, instead of using the timer arch protocol.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Zhang Lubo <lubo.zhang@intel.com>
Cc: Ni Ruiyu <ruiyu.ni@intel.com>
Cc: Ye Ting <ting.ye@intel.com>
Cc: Fu Siyuan <siyuan.fu@intel.com>
Reviewed-by: Fu Siyuan <siyuan.fu@intel.com>