snd-firewire-lib: [broken stream] add leaving the latest continuous packets in buffer

If there is a need to re-order packets between each callbacks, we must force to
process the latest packets of current callback in next callback.

This commit is a trial. By leaving the latest continuous packets in buffer.

But actually this take juju to stop next callback. I think all of the queued
packet with headers in a callback should be processed and queued for next
cycle. I need to find the other way for this purpose.