net: igb: fix the start time for periodic output signals

When programming the start of a periodic output, the code wrongly places
the seconds value into the "low" register and the nanoseconds into the
"high" register.  Even though this is backwards, it slipped through my
testing, because the re-arming code in the interrupt service routine is
correct, and the signal does appear starting with the second edge.

This patch fixes the issue by programming the registers correctly.

Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Acked-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>