Nt32Pkg.dsc: Add flag to control HTTP connections

Nt32Pkg.dsc: Add flag to control HTTP connections

v3:
* Correct the commits grammar

v2:
* Rename the flag.

This flag is to overwrite the value of PcdAllowHttpConnections,
then the platform can make a decision whether to allow HTTP
connections or not.

Cc: Ye Ting <ting.ye@intel.com>
Cc: Fu Siyuan <siyuan.fu@intel.com>
Cc: Ruiyu Ni <ruiyu.ni@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Cc: Kinney Michael D <michael.d.kinney@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Wu Jiaxin <jiaxin.wu@intel.com>
Reviewed-by: Ye Ting <ting.ye@intel.com>
Reviewed-by: Fu Siyuan <siyuan.fu@intel.com>
Reviewed-by: Gary Lin <glin@suse.com>