NetworkPkg: Fix incorrect buffer free in HttpDxe

NetworkPkg: Fix incorrect buffer free in HttpDxe

FragmentBuffer of each TcpWrap in HttpDxe should not be
freed in HttpTcpTokenCleanup(). This buffer points to
HttpMsg body actually, which is the responsibility of the
caller to allocate a buffer for Body.

Cc: Ye Ting <ting.ye@intel.com>
Cc: Fu Siyuan <siyuan.fu@intel.com>
Cc: Zhang Lubo <lubo.zhang@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jiaxin Wu <jiaxin.wu@intel.com>
Reviewed-by: Ye Ting <ting.ye@intel.com>