NetworkPkg/IScsiDxe: Add IPv6 support condition check.

NetworkPkg/IScsiDxe: Add IPv6 support condition check.

Base on the request of https://bugzilla.tianocore.org/show_bug.cgi?id=710,
we provide this patch to IPv6 condition check by leveraging AIP Protocol.

Cc: Karunakar P <karunakarp@amiindia.co.in>
Cc: Ye Ting <ting.ye@intel.com>
Cc: Fu Siyuan <siyuan.fu@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Karunakar P <karunakarp@amiindia.co.in>
Signed-off-by: Wu Jiaxin <jiaxin.wu@intel.com>
Reviewed-by: Karunakar p <karunakarp@amiindia.co.in>
Reviewed-by: Wu Jiaxin <jiaxin.wu@intel.com>