[burtc] Fix obc crash due to stack overflow inside burtc worker task.
[burtc] Fix obc crash due to stack overflow inside burtc worker task.

Problem was caused by the fact that timer's service notification routine
was executed inside burtc worker task context which did not have enough
stack space allocated to accomodate entire timer service functionality,
saving current time to flash memory in particular.

PW-Sat2/PWSat2OBC,PW-Sat2/PWSat2OBC,PW-Sat2/PWSat2OBC,PW-Sat2/PWSat2OBC