libnm: introduce NMTernary enum

Add a new enum that can be used where we need a boolean value that can
be overridden globally.

libnm-core/nm-dbus-interface.h

@@ -991,4 +991,20 @@ typedef enum { /*< flags >*/
 	NM_SETTINGS_UPDATE2_FLAG_BLOCK_AUTOCONNECT          = (1LL <<  5),
 } NMSettingsUpdate2Flags;
 
+/**
+ * NMTernary:
+ * @NM_TERNARY_DEFAULT: use the globally-configured default value.
+ * @NM_TERNARY_FALSE: the option is disabled.
+ * @NM_TERNARY_TRUE: the option is enabled.
+ *
+ * An boolean value that can be overridden by a default.
+ *
+ * Since: 1.14
+ **/
+typedef enum {
+	NM_TERNARY_DEFAULT = -1,
+	NM_TERNARY_FALSE = 0,
+	NM_TERNARY_TRUE = 1,
+} NMTernary;
+
 #endif /* __NM_DBUS_INTERFACE_H__ */

libnm/libnm.ver

@@ -1386,4 +1386,5 @@ global:
 	nm_device_wpan_get_type;
 	nm_setting_6lowpan_get_type;
 	nm_setting_wpan_get_type;
+	nm_ternary_get_type;
 } libnm_1_12_0;