vdpa_sim_blk: make vdpasim_blk_check_range usable by other requests

Next patches will add handling of other requests, where will be
useful to reuse vdpasim_blk_check_range().
So let's make it more generic by adding the `max_sectors` parameter,
since different requests allow different numbers of maximum sectors.

Let's also print the messages directly in vdpasim_blk_check_range()
to avoid duplicate prints.

Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Message-Id: <20220811083632.77525-3-sgarzare@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>