clock_readonly option is a list of clocks which
sfptpd should never synchronize or adjust.
This option can be used, for example, to prevent
adjusting the system clock when running alongside
chronyd in such a configuration will synchronize the system
clock_readonly [name | mac-address | clock-id | interface]
Specifies a set of clocks that
sfptpd should never step or slew, under any circumstance.