Bug fixes, send/receive debug logs and Unsigned 24 support

[TzviRonen]

Changes:

• Added test if callback exist before removing it from network subscribers.
• Added to sdo client and sdo server, send and receive debug logs.
• Added pause time before retrying send_request in sdo client request_response.
• Fixed the var len calculation in pdo base get_data. This one took me hours to debug..
• Added support for Unsigned 24 data types.