ptp: Work around bug in ptpd in default configuration
ptpd is defaulting to the hybrid mode, and was sending invalid multicast PTP messages in that configuration until ce96c742a88792a8d92deebaf03927e1b367f4a9. While this commit was made in 2015 there was no release in the meantime.
Work around this by detecting this case and defaulting to the default values for the given intervals as given by the PTP standard.