ShellPkg: Fix 'ping' command Ip4 receive flow.

ShellPkg: Fix 'ping' command Ip4 receive flow.

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=2032

'ping' command's receive flow utilizes a single Rx token which it
attempts to reuse before recycling the previously received packet.
This causes a situation where under ICMP traffic,
Ping6OnEchoReplyReceived() function will receive an already
recycled packet with EFI_SUCCESS token status and finally
dereference invalid pointers from RxData structure.

Cc: Ray Ni <ray.ni@intel.com>
Cc: Zhichao Gao <zhichao.gao@intel.com>
Signed-off-by: Maciej Rabeda <maciej.rabeda@linux.intel.com>
Reviewed-by: Siyuan Fu <siyuan.fu@intel.com>
Acked-by: Zhichao Gao <zhichao.gao@intel.com>