Multi frame (#6)

Multi frame (#6)

* increase payload size just for diag responses to support multi-frame responses. limited to 255 bytes for now.

* not all diag requests with modes greater than 0xa have a 2 byte pid. need to check was pid_length should be based on the size of the pid.

* remove line that does nothing.

* add multi_frame field to DiagnosticResponse and update based on IsoTpMessage. Need this upstream for timeout calls specific to multi frame.

* update isotp-c submodule.

* update autoset_pid tests. check that pid_length is dynamically set based on pid value. adjust other tests to use 2-byte pid for enhanced diagnostic mode requests.

* add test for multi-frame response.

* update changelog.