Handle ERR_CMD_UNKNOWN in GET_COMM_MODE_INFO

[chrisoro]

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [x] I have read the CONTRIBUTING document.
• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] I have added tests to cover my changes.
• [x] All new and existing tests passed.

According to the XCP spec, the GET_COMM_MODE_INFO command is optional. I noticed that an error handler for ERR_CMD_UNKNOWN was present for all other optional commands, but missing for this one. So, I've added it accordingly.

[christoph2]

OK, was missing. Nobody is required to use (but everybody should use) the following start-up sequence...

 x.connect()
 if x.slaveProperties.optionalCommMode:
     x.getCommModeInfo()