Add tun inbound for linux

common/tun/gvisor_linux.go

@@ -0,0 +1,16 @@
+//go:build linux
+
+package tun
+
+import (
+	"gvisor.dev/gvisor/pkg/tcpip/link/fdbased"
+	"gvisor.dev/gvisor/pkg/tcpip/stack"
+)
+
+func NewEndpoint(tunFd uintptr, tunMtu uint32) (stack.LinkEndpoint, error) {
+	return fdbased.New(&fdbased.Options{
+		FDs:                []int{int(tunFd)},
+		MTU:                tunMtu,
+		PacketDispatchMode: fdbased.PacketMMap,
+	})
+}