sync lost on slave every ~49.7 days

Due to the bug in PPSI, WR switch lost synchronization every ~49.7 days of master uptime. Usually, slave synchronizes back and enters TRACK_PHASE. However, sometimes when the synchronization is lost, additionally due to bug #240 (closed), on slave PPSI's servo may stop updating. When this happens the servo stuck in a valid state.

Related to #240 (closed), #235 (closed). The details are described in ppsi#31.

Probably not related to #236.

Only firmware v6.0 is affected with this bug. When switch is not able to synchronize again it is necessary to restart PPSI or do link down/up (by ifconfig or unplug/plug a fiber).

Restarting PPSI prior to the problematic uptime (multiply of ~49.7 days), does not prevent the error to occur. What counts is the uptime of a switch not the uptime of PPSI. The only known way to prevent a switch to lost sync at predicted time is to reboot the switch and/or update to newer firmware (at least v6.0.1).