NetworkPkg:HttpDxe:Consume DxeHttpLib API changes

NetworkPkg:HttpDxe:Consume DxeHttpLib API changes

HttpGenRequestString is updated to HttpGenRequestMessage,
with an additional argument. This patch updates the caller
of the DxeHttpLib API. Also, we will avoid adding any '\0'
to the string, which was added to make AsciiStrLen to
work on the string.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Nagaraj Hegde <nagaraj-p.hegde@hpe.com>
Reviewed-by: Fu Siyuan <siyuan.fu@intel.com>
Reviewed-by: Samer El-Haj-Mahmoud <elhaj@hpe.com>