CLA: TCPSPP: Drop SPPs with unknown APID before parsing timecode
We do not need to parse the timecode to drop SPP frames that do not belong to us. This makes the SPP parser return on every change of its internal state (as it is called again by the CLA methods, this is a totally valid mode of operation) and check the APID early in the CLA methods.
By that we also support receiving SPPs that use different formats to other APIDs (e.g., without any timecode in case we are expecting a timecode).