core: rename NM_PLATFORM_ROUTE_METRIC_DEFAULT to NM_PLATFORM_ROUTE_METRIC_DEFAULT_IP6

For IPv4, iproute for example defaults to a metric of 0.
Hence, the name NM_PLATFORM_ROUTE_METRIC_DEFAULT was misleading.

Also add a NM_PLATFORM_ROUTE_METRIC_DEFAULT_IP4 define for completeness.

https://bugzilla.gnome.org/show_bug.cgi?id=740780

src/NetworkManagerUtils.h

@@ -39,14 +39,14 @@ const struct in6_addr *nm_utils_ip6_address_clear_host_address (struct in6_addr
  * @metric: the route metric
  *
  * For IPv6 route, kernel treats the value 0 as IP6_RT_PRIO_USER (1024).
- * Thus, when comparing metric (values), we want to treat zero as NM_PLATFORM_ROUTE_METRIC_DEFAULT.
+ * Thus, when comparing metric (values), we want to treat zero as NM_PLATFORM_ROUTE_METRIC_DEFAULT_IP6.
  *
  * Returns: @metric, if @metric is not zero, otherwise 1024.
  */
 static inline guint32
 nm_utils_ip6_route_metric_normalize (guint32 metric)
 {
-	return metric ? metric : 1024 /*NM_PLATFORM_ROUTE_METRIC_DEFAULT*/;
+	return metric ? metric : 1024 /*NM_PLATFORM_ROUTE_METRIC_DEFAULT_IP6*/;
 }
 
 int nm_spawn_process (const char *args);

src/devices/nm-device.c

@@ -669,7 +669,7 @@ nm_device_get_priority (NMDevice *self)
 	 *
 	 * For comparison, note that iproute2 by default adds IPv4 routes with
 	 * metric 0, and IPv6 routes with metric 1024. The latter is the IPv6
-	 * "user default" in the kernel (NM_PLATFORM_ROUTE_METRIC_DEFAULT).
+	 * "user default" in the kernel (NM_PLATFORM_ROUTE_METRIC_DEFAULT_IP6).
 	 * In kernel, the full uint32_t range is available for route
 	 * metrics (except for IPv6, where 0 means 1024).
 	 */

src/platform/nm-platform.h

@@ -184,9 +184,15 @@ typedef union {
 #undef __NMPlatformIPAddress_COMMON
 
 
-/* Adding an IPv6 route with metric 0, kernel translates to IP6_RT_PRIO_USER (1024).
- * Thus, the value is not choosen arbitraily, but matches kernel IPv6 default. */
-#define NM_PLATFORM_ROUTE_METRIC_DEFAULT 1024
+/* Default value for adding an IPv4 route. This is also what iproute2 does.
+ * Note that contrary to IPv6, you can add routes with metric 0 and it is even
+ * the default.
+ */
+#define NM_PLATFORM_ROUTE_METRIC_DEFAULT_IP4 0
+
+/* Default value for adding an IPv6 route. This is also what iproute2 does.
+ * Adding an IPv6 route with metric 0, kernel translates to IP6_RT_PRIO_USER (1024). */
+#define NM_PLATFORM_ROUTE_METRIC_DEFAULT_IP6 1024
 
 /* For IPv4, kernel adds a device route (subnet routes) with metric 0 when user
  * configures addresses. */