CVE-2025-21666 vsock: prevent null-ptr-deref in vsock_*[has_data|has_space]

In the Linux kernel, the following vulnerability has been resolved: vsock: prevent null-ptr-deref in vsockhasdata|hasspace Recent reports have shown how we sometimes call vsockhasdata when a vsock socket has been de-assigned from a transport see attached links, but we shouldn't. Previous commits...