ShellPkg:Ping: Ping command hangs with intermittent packet losses

ShellPkg:Ping: Ping command hangs with intermittent packet losses

When we have intermittent loss of packets, ping command doesnt
return to Shell prompt. It keeps looping in the while (Status
==EFI_NOT_READY) since Private->RxCount will never reach
Private->SendNum. Addresses the issue with the use of a new varibale
in the PRIVATE structure.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Hegde, Nagaraj P <nagaraj-p.hegde@hpe.com>
Reviewed-by: Sriram Subramanian <sriram-s@hpe.com>
Reviewed-by: Jaben Carsey <jaben.carsey@intel.com>