vhost: notify virtq file descriptor update

vhost: notify virtq file descriptor update

When virtq call or kick file descriptors are changed in the device
configuration when the queue is ready, the application and the vDPA
driver should be notified to be aligned to the new file descriptors.

Notify the state to be disabled before the file descriptor update and
return it back to be enabled after the update.

Signed-off-by: Matan Azrad <matan@mellanox.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Reviewed-by: Chenbo Xia <chenbo.xia@intel.com>