fix(netwatch): detect IPv6 default routes on Linux

netwatch/src/interfaces/linux.rs

@@ -41,9 +41,11 @@ pub enum Error {
 }
 
 pub async fn default_route() -> Option<DefaultRouteDetails> {
-    let route = default_route_proc().await;
-    if let Ok(route) = route {
-        return route;
+    // /proc/net/route only contains IPv4 routes. If it finds one, return it.
+    // If it returns Ok(None) (no IPv4 default route) or Err (file unreadable),
+    // fall through to netlink which checks both IPv4 and IPv6.
+    if let Ok(Some(route)) = default_route_proc().await {
+        return Some(route);
     }
 
     #[cfg(target_os = "android")]

netwatch/tests/patchbay.rs

@@ -51,7 +51,6 @@ async fn default_route_v4_only() -> TestResult {
 
 /// Netwatch detects a default route on a v6-only network.
 #[tokio::test]
-#[ignore = "default_route() does not fall through to netlink when /proc/net/route has no IPv4 default"]
 async fn default_route_v6_only() -> TestResult {
     let state = state_for_routed_device(IpSupport::V6Only).await?;
 
@@ -75,7 +74,6 @@ async fn default_route_dual_stack() -> TestResult {
 /// After replugging from a v4 router to a v6 router, netwatch detects the new
 /// default route.
 #[tokio::test]
-#[ignore = "default_route() does not fall through to netlink when /proc/net/route has no IPv4 default"]
 async fn default_route_after_replug_v4_to_v6() -> TestResult {
     let lab = Lab::new().await?;
     let v4_router = lab