The ntp_gettime implementation of NTP exports the tai field the kernel
now produces. This requires an ABI change since the ntptimeval structure
changed. Upstream kept the same name, there is nothing to do. This
patch changes the ntptimeval structure but keeps the old ntp_gettime
definition. A new ntp_gettimex function which is transparently invoked
through the old name is introduced. This has the advantage that even
object files can remain compatible. This wouldn't be the case if
symbol versioning would be used to overload the name ntp_gettime.
