carp, provide a way to 'permanently' set carp to 'maintenance mode' (advskew 254) persisting a reboot
Option to set CARP interfaces to 'maintenance mode', persisting through a reboot so the primary machines stays as backup/inactive.
This is required when there are some problems (possibly with the hardware) and the primary machine needs to be booted and checked again before becoming 'master'. Currently it will take back the master state during reboot even though there might still be problems or some re-configuring to do.

p.s. it is for some reason not possible to reset advskew back to '0'.. should that number be removed as an option, and use 1 as a minimal value ?
Merge pull request #1041 from PiBa-NL/carp_maintenance_2.2

carp, provide a way to 'permanently' set carp to 'maintenance mode' (advskew 254) persisting a reboot