tun/netstack: bump to latest gvisor

To build with go1.19, gvisor needs
99325baf ("Bump gVisor build tags to go1.19").

However gvisor.dev/gvisor/pkg/tcpip/buffer is no longer available,
so refactor to use gvisor.dev/gvisor/pkg/tcpip/link/channel directly.

Signed-off-by: Shengjing Zhu <[email protected]>
Signed-off-by: Jason A. Donenfeld <[email protected]>

Author: zhsj

tun/netstack/go.mod

@@ -5,7 +5,7 @@ go 1.18
 require (
 	golang.org/x/net v0.0.0-20220225172249-27dd8689420f
 	golang.zx2c4.com/wireguard v0.0.0-20220316235147-5aff28b14c24
-	gvisor.dev/gvisor v0.0.0-20211020211948-f76a604701b6
+	gvisor.dev/gvisor v0.0.0-20220817001344-846276b3dbc5
 )
 
 require (