wgengine/wglog: quieten WireGuard logs for allowedips

An increasing number of users have very large subnet route
configurations, which can produce very large amounts of log data when
WireGuard is reconfigured. The logs don't contain the actual routes, so
they're largely useless for diagnostics, so we'll just suppress them.

Fixes tailscale/corp#17532

Signed-off-by: James Tucker <james@tailscale.com>

wgengine/wglog/wglog_test.go

@@ -64,6 +64,23 @@ func TestLogger(t *testing.T) {
 	}
 }
 
+func TestSuppressLogs(t *testing.T) {
+	var logs []string
+	logf := func(format string, args ...any) {
+		logs = append(logs, fmt.Sprintf(format, args...))
+	}
+	x := wglog.NewLogger(logf)
+	x.DeviceLogger.Verbosef("pass")
+	x.DeviceLogger.Verbosef("UAPI: Adding allowedip")
+
+	if len(logs) != 1 {
+		t.Fatalf("got %d logs, want 1", len(logs))
+	}
+	if logs[0] != "wg: [v2] pass" {
+		t.Errorf("got %q, want \"wg: [v2] pass\"", logs[0])
+	}
+}
+
 func stringer(s string) stringerString {
 	return stringerString(s)
 }