migration/multifd: use pages->allocated instead of the static max

migration/multifd: use pages->allocated instead of the static max

multifd_send_fill_packet() prepares meta data for following pages to
transfer. It would be more proper to fill pages->allocated instead of
static max value, especially we want to support flexible packet size.

Signed-off-by: Wei Yang <richardw.yang@linux.intel.com>
Message-Id: <20191011085050.17622-3-richardw.yang@linux.intel.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>