NetworkPkg: Add old IPv4_DEVICE_PATH and IPv6_DEVICE_PATH support

NetworkPkg: Add old IPv4_DEVICE_PATH and IPv6_DEVICE_PATH support

GatewayIpAddress and SubnetMask do not exist in old IPv4_DEVICE_PATH,
IPAddressOrigin, PrefixLength and GatewayIPAddress do not exist in old
IPv6_DEVICE_PATH. This will lead new IScsiDxe to error without updating
IPv4_DEVICE_PATH and IPv6_DEVICE_PATH in system.

Following UEFI2.5 spec of IPv4_DEVICE_PATH do a check before accessing
fields only defined in new version's IPv4_DEVICE_PATH, and revise the same
issue for IPv6_DEVICE_PATH in Iscsi driver.

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: fanwang2 <fan.wang@intel.com>
Reviewed-by: Ye Ting <ting.ye@intel.com>
[lersek@redhat.com: rewrapped commit message]
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@18056 6f19259b-4bc3-4df7-8a09-765794883524