doc: update NEWS

The kernel requires in the ADJ_SETOFFSET | ADJ_NANO mode that the
timex.time.tv_usec value is smaller than 10^9 nanosecond, which wasn't
the case with a negative integer offset (e.g. inserted leap second).

NEWS

@@ -1,3 +1,10 @@
+New in version 2.1.1
+====================
+
+Bug fixes
+---------
+* Fix clock stepping by integer number of seconds on Linux
+
 New in version 2.1
 ==================
 

wrap_adjtimex.c

@@ -193,12 +193,12 @@ TMX_ApplyStepOffset(double offset)
   struct timex txc;
 
   txc.modes = ADJ_SETOFFSET | ADJ_NANO;
-  if (offset >= 0) {
+  txc.time.tv_sec = offset;
-    txc.time.tv_sec = offset;
-  } else {
-    txc.time.tv_sec = offset - 1;
-  }
   txc.time.tv_usec = 1.0e9 * (offset - txc.time.tv_sec);
+  if (txc.time.tv_usec < 0) {
+    txc.time.tv_sec--;
+    txc.time.tv_usec += 1000000000;
+  }
 
   return adjtimex(&txc);
 }