cmd/stunstamp: refactor connection construction (#13110)

getConns() is now responsible for returning both stable and unstable
conns. conn and measureFn are now passed together via connAndMeasureFn.
newConnAndMeasureFn() is responsible for constructing them.

TCP measurement timeouts are adjusted to more closely match netcheck.

Updates tailscale/corp#22114

Signed-off-by: Jordan Whited <jordan@tailscale.com>

cmd/stunstamp/stunstamp_default.go

@@ -20,8 +20,28 @@ func measureSTUNRTTKernel(conn io.ReadWriteCloser, hostname string, dst netip.Ad
 	return 0, errors.New("unimplemented")
 }
 
-func protocolSupportsKernelTS(_ protocol) bool {
-	return false
+func getProtocolSupportInfo(p protocol) protocolSupportInfo {
+	switch p {
+	case protocolSTUN:
+		return protocolSupportInfo{
+			kernelTS:    false,
+			userspaceTS: true,
+			stableConn:  true,
+		}
+	case protocolHTTPS:
+		return protocolSupportInfo{
+			kernelTS:    false,
+			userspaceTS: true,
+			stableConn:  true,
+		}
+	case protocolTCP:
+		return protocolSupportInfo{
+			kernelTS:    true,
+			userspaceTS: false,
+			stableConn:  true,
+		}
+	}
+	return protocolSupportInfo{}
 }
 
 func setSOReuseAddr(fd uintptr) error {