This function speeds up or slows down the system clock in order to make a gradual adjustment. This ensures
that the calendar time reported by the system clock is always monotonically increasing, which might not happen
if you simply set the clock.
The delta argument specifies a relative adjustment to be made to the clock time. If negative, the system clock is
slowed down for a while until it has lost this much elapsed time. If positive, the system clock is speeded up for a
while.
If the olddelta argument is not a null pointer, the adjtime function returns information about any previous time
adjustment that has not yet completed.
The return value is 0 on success and -1 on failure.
To stop the adjustement, call the function settimeofday(current_time).
In some cases (when RTC register reads are performed from the APP CPU), a write to FRC_TIMER_INT_REG may be lost on the bus.
Writing to another DPORT register immediately before or after that works around the issue.
We write one dummy value to an address which doesn’t have any register associated with it.
Fixes https://github.com/espressif/arduino-esp32/issues/120
