Updates for time keeping:

  - Fix a couple of issues in the NTP code where user supplied values are
    neither sanity checked nor clamped to the operating range. This results
    in integer overflows and eventualy NTP getting out of sync.

    According to the history the sanity checks had been removed in favor of
    clamping the values, but the clamping never worked correctly under all
    circumstances. The NTP people asked to not bring the sanity checks back
    as it might break existing applications.

    Make the clamping work correctly and add it where it's missing

  - If adjtimex() sets the clock it has to trigger the hrtimer subsystem so
    it can adjust and if the clock was set into the future expire timers if
    needed. The caller should provide a bitmask to tell hrtimers which
    clocks have been adjusted. adjtimex() uses not the proper constant and
    uses CLOCK_REALTIME instead, which is 0. So hrtimers adjusts only the
    clocks, but does not check for expired timers, which might make them
    expire really late. Use the proper bitmask constant instead.