ram.c: Call update_compress_thread_counts from compress_send_queued_data

This makes the core compress code more independend from ram.c.

Signed-off-by: Lukas Straub <lukasstraub2@web.de>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>