util: TristateBool and TristateSwitch are interchangeable

It may be useful in some cases to call TristateSwitch helper with TristateBool.
Document that enum values equivalency in the code.
Signed-off-by: NMarc-André Lureau <marcandre.lureau@redhat.com>

src/util/virutil.h

@@ -236,10 +236,15 @@ typedef enum {
     VIR_TRISTATE_SWITCH_LAST
 } virTristateSwitch;
 
-
 VIR_ENUM_DECL(virTristateBool)
 VIR_ENUM_DECL(virTristateSwitch)
 
+/* the two enums must be in sync to be able to use helpers interchangeably in
+ * some special cases */
+verify((int)VIR_TRISTATE_BOOL_YES == (int)VIR_TRISTATE_SWITCH_ON);
+verify((int)VIR_TRISTATE_BOOL_NO == (int)VIR_TRISTATE_SWITCH_OFF);
+verify((int)VIR_TRISTATE_BOOL_ABSENT == (int)VIR_TRISTATE_SWITCH_ABSENT);
+
 unsigned int virGetListenFDs(void);
 
 long virGetSystemPageSize(void);