hostinet: fix fd leak in fdnotifier for VFS2

When we failed to create the new socket after adding the fd to
fdnotifier, we should remove the fd from fdnotifier, because we
are going to close the fd directly.

Fixes: #3241

Signed-off-by: Tiwei Bie <tiwei.btw@antgroup.com>

pkg/sentry/socket/hostinet/socket_vfs2.go

@@ -71,6 +71,7 @@ func newVFS2Socket(t *kernel.Task, family int, stype linux.SockType, protocol in
 		DenyPWrite:        true,
 		UseDentryMetadata: true,
 	}); err != nil {
+		fdnotifier.RemoveFD(int32(s.fd))
 		return nil, syserr.FromError(err)
 	}
 	return vfsfd, nil