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