NetworkPkg/IpSecDxe: Fix issue to parse SA Payload.

NetworkPkg/IpSecDxe: Fix issue to parse SA Payload.

Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=1251

*v2: Correct the type of parameters in Ikev2ParseProposalData(), and refined
the corresponding description.

IpSecDxe failed to create the Child SA during parsing SA Payload, the issue
was caused by the below commit:

SHA-1: 1e0db7b11987d0ec93be7dfe26102a327860fdbd
* MdeModulePkg/NetworkPkg: Checking for NULL pointer before use.

In above commit, it changed the value of IsMatch in Ikev2ChildSaParseSaPayload()
to FALSE. That's correct but it exposed the potential bug in to match the correct
proposal Data, which will cause the issue happen.

Cc: Fu Siyuan <siyuan.fu@intel.com>
Cc: Ye Ting <ting.ye@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Wu Jiaxin <jiaxin.wu@intel.com>
Reviewed-by: Ye Ting <ting.ye@intel.com>