[crosvm] breaking change in vhost-user protocol for GPU and FS devices

[Frederick Mayle]

We are switching to standardized versions of the SHMEM_MAP, SHMEM_UNMAP, and GET_SHARED_MEMORY_REGIONS features in https://crrev.com/c/7260977.

This will cause a problem if you use crosvm (VMM or vhost-user backend) together with a non-crosvm VMM or vhost-user backend that implemented the same non-standard features (or, less likely, if you have version skew between your crosvm VMM and crosvm vhost-user backend binaries).