Update vfs2 socket TODOs.

Three updates:
- Mark all vfs2 socket syscalls as supported.
- Use the same dev number and ino number generator for all types of sockets,
  unlike in VFS1.
- Do not use host fd for hostinet metadata.

Fixes #1476, #1478, #1484, 1485, #2017.

PiperOrigin-RevId: 309994579

pkg/sentry/socket/netstack/netstack_vfs2.go

@@ -22,6 +22,7 @@ import (
 	"gvisor.dev/gvisor/pkg/sentry/fsimpl/sockfs"
 	"gvisor.dev/gvisor/pkg/sentry/inet"
 	"gvisor.dev/gvisor/pkg/sentry/kernel"
+	"gvisor.dev/gvisor/pkg/sentry/socket"
 	"gvisor.dev/gvisor/pkg/sentry/socket/netfilter"
 	"gvisor.dev/gvisor/pkg/sentry/vfs"
 	"gvisor.dev/gvisor/pkg/syserr"
@@ -41,6 +42,8 @@ type SocketVFS2 struct {
 	socketOpsCommon
 }
 
+var _ = socket.SocketVFS2(&SocketVFS2{})
+
 // NewVFS2 creates a new endpoint socket.
 func NewVFS2(t *kernel.Task, family int, skType linux.SockType, protocol int, queue *waiter.Queue, endpoint tcpip.Endpoint) (*vfs.FileDescription, *syserr.Error) {
 	if skType == linux.SOCK_STREAM {