The current virtqueue_avail_bytes() is oddly named, and checks if a
particular number of bytes are available in a vq. A better API is to
fetch the number of bytes available in the vq, and let the caller do
what's interesting with the numbers.
Introduce virtqueue_get_avail_bytes(), which returns the number of bytes
for buffers marked for both, in as well as out. virtqueue_avail_bytes()
is made a wrapper over this new function.
Signed-off-by: Amit Shah <amit.shah@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>