vmxnet3: Introduce 'x-old-msi-offsets' back-compat property

Following the previous patches, where vmxnet3's pci's msi/msix
capability offsets and msix's PBA table offsets have been changed, this
patch introduces a boolean property 'x-old-msi-offsets' to vmxnet3,
whose default is false.

Setting 'x-old-msi-offsets' to 'on' preserves the old offsets behavior,
which allows migration to older versions.

Signed-off-by: Shmulik Ladkani <shmulik.ladkani@ravellosystems.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

hw/net/vmxnet3.c

@@ -2593,6 +2593,8 @@ static const VMStateDescription vmstate_vmxnet3 = {
 
 static Property vmxnet3_properties[] = {
     DEFINE_NIC_PROPERTIES(VMXNET3State, conf),
+    DEFINE_PROP_BIT("x-old-msi-offsets", VMXNET3State, compat_flags,
+                    VMXNET3_COMPAT_FLAG_OLD_MSI_OFFSETS_BIT, false),
     DEFINE_PROP_END_OF_LIST(),
 };
 

include/hw/compat.h

@@ -2,7 +2,11 @@
 #define HW_COMPAT_H
 
 #define HW_COMPAT_2_5 \
-    /* empty */
+    {\
+        .driver   = "vmxnet3",\
+        .property = "x-old-msi-offsets",\
+        .value    = "on",\
+    },
 
 #define HW_COMPAT_2_4 \
     {\