libnet: Revert "Only check if route overlaps routes with scope: LINK"

This reverts commit ee9e526.

Route scope is used by the kernel to choose what source IP address
should be used when establishing an outbound connection. As such,
filtering routes based on their scope doesn't make sense.

Resolve #46615.

libnetwork/netutils/utils_linux.go

@@ -28,7 +28,7 @@ func CheckRouteOverlaps(toCheck *net.IPNet) error {
 		return err
 	}
 	for _, network := range networks {
-		if network.Dst != nil && network.Scope == netlink.SCOPE_LINK && NetworkOverlaps(toCheck, network.Dst) {
+		if network.Dst != nil && NetworkOverlaps(toCheck, network.Dst) {
 			return ErrNetworkOverlaps
 		}
 	}

libnetwork/netutils/utils_linux_test.go

@@ -49,11 +49,8 @@ func TestCheckRouteOverlaps(t *testing.T) {
 		routes := []netlink.Route{}
 		for _, addr := range routesData {
 			_, netX, _ := net.ParseCIDR(addr)
-			routes = append(routes, netlink.Route{Dst: netX, Scope: netlink.SCOPE_LINK})
+			routes = append(routes, netlink.Route{Dst: netX})
 		}
-		// Add a route with a scope which should not overlap
-		_, netX, _ := net.ParseCIDR("10.0.5.0/24")
-		routes = append(routes, netlink.Route{Dst: netX, Scope: netlink.SCOPE_UNIVERSE})
 		return routes, nil
 	}
 	defer func() { networkGetRoutesFct = nil }()
@@ -67,11 +64,6 @@ func TestCheckRouteOverlaps(t *testing.T) {
 	if err := CheckRouteOverlaps(netX); err == nil {
 		t.Fatal("10.0.2.0/24 and 10.0.2.0 should overlap but it doesn't")
 	}
-
-	_, netX, _ = net.ParseCIDR("10.0.5.0/24")
-	if err := CheckRouteOverlaps(netX); err != nil {
-		t.Fatal("10.0.5.0/24 and 10.0.5.0 with scope UNIVERSE should not overlap but it does")
-	}
 }
 
 func TestCheckNameserverOverlaps(t *testing.T) {