CVE-2024-43873

In the Linux kernel, the following vulnerability has been resolved:

vhost/vsock: always initialize seqpacket_allow

There are two issues around seqpacket_allow:
1. seqpacket_allow is not initialized when socket is
created. Thus if features are never set, it will be
read uninitialized.
2. if VIRTIO_VSOCK_F_SEQPACKET is set and then cleared,
then seqpacket_allow will not be cleared appropriately
(existing apps I know about don't usually do this but
it's legal and there's no way to be sure no one relies
on this).

To fix:
- initialize seqpacket_allow after allocation
- set it unconditionally in set_features