When WR PTP Core is set in GrandMaster mode it aligns its nanosecond
counter to 1-PPS and 10MHz coming from external source. When user wants
to set seconds counter to a desired value (with _time set_ command), the
nanosecond counter was also set (zeroed) causing additional (random)
offset to the external source. The commit adds _time setsec_ and _time
setnsec_ for setting only seconds or nanoseconds counter without
affecting the other one. Now, when user wants to set current time on a
GrandMaster Node he has to call _time setsec_ command after _mode gm_