Control offset correction rate in Linux driver

The kernel currently doesn't support a linear adjustment with
programmable rate, extend the use of the kernel PLL with locked
frequency instead.

Set the PLL time constant according to the correction time corresponding
to the correction rate and corrected offset.

On kernels with nano PLL adjtime() is no longer used.

wrap_adjtimex.c

@@ -207,13 +207,13 @@ TMX_EnableNanoPLL(void)
 }
 
 int
-TMX_ApplyPLLOffset(long offset)
+TMX_ApplyPLLOffset(long offset, long constant)
 {
   struct timex txc;
 
   txc.modes = ADJ_OFFSET | ADJ_TIMECONST | ADJ_NANO;
   txc.offset = offset;
-  txc.constant = 0;
+  txc.constant = constant;
   return adjtimex(&txc);
 }