qemu: use stream netdev with reconnect for socketVMNet networking

Use -netdev stream instead of legacy -netdev socket for socketVMNet
networking on macOS Intel (QEMU backend), with version-appropriate
reconnect. Applies to all socketVMNet modes (bridged, shared, host).

  QEMU >= 9.2: stream with reconnect-ms=500
  QEMU 8.0-9.1: stream with reconnect=1 (seconds granularity)
  QEMU 7.2-7.9: stream without reconnect
  QEMU < 7.2: fall back to socket (no stream support)

The stream backend connects directly to the socket_vmnet UNIX socket,
eliminating the pre-dialed fd approach. When reconnect is available,
QEMU automatically re-establishes the connection after link failures,
recovering VM networking without manual restart.

In testing, stream netdev showed ~2x throughput improvement over
legacy socket netdev (~1.84 Gbits/sec vs ~970 Mbits/sec).

Feature-detected via -netdev help output; version checked for the
reconnect parameter which was renamed from reconnect (8.0) to
reconnect-ms (9.2) and the old form removed in 10.2.

Signed-off-by: Lon C. Lundgren <lon@ocelot.net>

Author: loncharles

pkg/driver/qemu/qemu.go

@@ -816,9 +816,17 @@ func Cmdline(ctx context.Context, cfg Config) (exe string, args []string, err er
 				if err != nil {
 					return "", nil, err
 				}
-				args = append(args, "-netdev", fmt.Sprintf("socket,id=net%d,fd={{ fd_connect %q }}", i+1, sock))
-				// TODO: should we also validate that the socket exists, or do we rely on the
-				// networks reconciler to throw an error when the network cannot start?
+				if strings.Contains(string(features.NetdevHelp), "stream") {
+					netdev := fmt.Sprintf("stream,id=net%d,server=off,addr.type=unix,addr.path=%s", i+1, sock)
+					if !version.LessThan(*semver.New("9.2.0")) {
+						netdev += ",reconnect-ms=500"
+					} else if !version.LessThan(*semver.New("8.0.0")) {
+						netdev += ",reconnect=1"
+					}
+					args = append(args, "-netdev", netdev)
+				} else {
+					args = append(args, "-netdev", fmt.Sprintf("socket,id=net%d,fd={{ fd_connect %q }}", i+1, sock))
+				}
 			}
 		} else if nw.Socket != "" {
 			args = append(args, "-netdev", fmt.Sprintf("socket,id=net%d,fd={{ fd_connect %q }}", i+1, nw.Socket))