sandbox: support vsock connection to task api

Signed-off-by: Abel Feng <fshb1988@gmail.com>

vendor/github.com/mdlayher/socket/accept4.go

@@ -0,0 +1,15 @@
+//go:build dragonfly || freebsd || illumos || linux
+// +build dragonfly freebsd illumos linux
+
+package socket
+
+import (
+	"golang.org/x/sys/unix"
+)
+
+const sysAccept = "accept4"
+
+// accept wraps accept4(2).
+func accept(fd, flags int) (int, unix.Sockaddr, error) {
+	return unix.Accept4(fd, flags)
+}