ioapic: Add support for qemu-kvm's vmstate v2

qemu-kvm carries the IOAPIC base address in its v2 vmstate. We only
support the default base address so far, and saving even that in the
device state was rejected.

Add a padding field to be able to read qemu-kvm's old state, but
increase our version to 3, indicating that we are not saving a valid
address. This also gives downstream the chance to change to stop
evaluating the base_address and move to v3 as well.
Signed-off-by: NJan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

hw/ioapic.c

@@ -244,13 +244,14 @@ static int ioapic_post_load(void *opaque, int version_id)
 
 static const VMStateDescription vmstate_ioapic = {
     .name = "ioapic",
-    .version_id = 2,
+    .version_id = 3,
     .post_load = ioapic_post_load,
     .minimum_version_id = 1,
     .minimum_version_id_old = 1,
     .fields      = (VMStateField []) {
         VMSTATE_UINT8(id, IOAPICState),
         VMSTATE_UINT8(ioregsel, IOAPICState),
+        VMSTATE_UNUSED_V(2, 8), /* to account for qemu-kvm's v2 format */
         VMSTATE_UINT32_V(irr, IOAPICState, 2),
         VMSTATE_UINT64_ARRAY(ioredtbl, IOAPICState, IOAPIC_NUM_PINS),
         VMSTATE_END_OF_LIST()