ctdb: Introduce buffer.offset to avoid memmove

ctdb: Introduce buffer.offset to avoid memmove

The memmove operation is quite expensive, therefore,
a new buffer attribute "offset" is introduced to support
an optimized buffer processing.
The optimization is to "walk" through the buffer and process
each packet until the buffer is fully processed (empty)
without requiring any memmove.
Only if a packet is in-complete, the buffer content is moved
and the new data is read from the queue.
This way almost all memmove operations are eliminated.

Signed-off-by: Swen Schillig <swen@vnet.ibm.com>
Reviewed-by: Martin Schwenke <martin@meltin.net>
Reviewed-by: Christof Schmitt <cs@samba.org>