vhost-user: remove VirtQ notifier restore

vhost-user: remove VirtQ notifier restore

Notifier set when vhost-user backend asks qemu to mmap an FD and
offset. When vhost-user backend restart or getting killed, VQ notifier
FD and mmap addresses become invalid. After backend restart, MR contains
the invalid address will be restored and fail on notifier access.

On the other hand, qemu should munmap the notifier, release underlying
hardware resources to enable backend restart and allocate hardware
notifier resources correctly.

Qemu shouldn't reference and use resources of disconnected backend.

This patch removes VQ notifier restore, uses the default vhost-user
notifier to avoid invalid address access.

After backend restart, the backend should ask qemu to install a hardware
notifier if needed.

Fixes: 44866521bd6e ("vhost-user: support registering external host notifiers")
Cc: [email protected]
Signed-off-by: Xueming Li <[email protected]>
Message-Id: <20220207071929[email protected]>
Reviewed-by: Michael S. Tsirkin <[email protected]>
Signed-off-by: Michael S. Tsirkin <[email protected]>