vhost_net: configure all host notifiers in a single MR transaction

vhost_net: configure all host notifiers in a single MR transaction

This allows the vhost_net device which has multiple virtqueues to batch
the setup of all its host notifiers. This significantly reduces the
vhost_net device starting and stoping time, e.g. the time spend
on enabling notifiers reduce from 630ms to 75ms and the time spend on
disabling notifiers reduce from 441ms to 45ms for a VM with 192 vCPUs
and 15 vhost-user-net devices (64vq per device) in our case.

Signed-off-by: zuoboqun <zuoboqun@baidu.com>
Message-Id: <20240816070835.8309-1-zuoboqun@baidu.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>