Set reference time to last sample instead of time on update

This is done mainly to fix reported root dispersion to include max clock
error after selecting another source without new sample.

reference.c

@@ -530,10 +530,10 @@ REF_SetReference(int stratum,
   double delta_freq1, delta_freq2;
   double skew1, skew2;
   double our_frequency;
-
   double abs_freq_ppm;
-
   double update_interval;
+  double elapsed;
+  struct timeval now;
 
   assert(initialised);
 
@@ -570,10 +570,13 @@ REF_SetReference(int stratum,
   else
     our_ref_ip.family = IPADDR_UNSPEC;
   our_ref_time = *ref_time;
-  our_offset = offset;
   our_root_delay = root_delay;
   our_root_dispersion = root_dispersion;
 
+  LCL_ReadCookedTime(&now, NULL);
+  UTI_DiffTimevalsToDouble(&elapsed, &now, ref_time);
+  our_offset = offset + elapsed * frequency;
+
   update_leap_status(leap);
 
   /* Eliminate updates that are based on totally unreliable frequency
@@ -627,14 +630,14 @@ REF_SetReference(int stratum,
 
   abs_freq_ppm = LCL_ReadAbsoluteFrequency();
 
-  write_log(ref_time,
+  write_log(&now,
             our_ref_ip.family != IPADDR_UNSPEC ? UTI_IPToString(&our_ref_ip) : UTI_RefidToString(our_ref_id),
             our_stratum,
             abs_freq_ppm,
             1.0e6*our_skew,
             our_offset);
 
-  UTI_DiffTimevalsToDouble(&update_interval, ref_time, &last_ref_update);
+  UTI_DiffTimevalsToDouble(&update_interval, &now, &last_ref_update);
 
   if (drift_file) {
     /* Update drift file at most once per hour */
@@ -650,7 +653,7 @@ REF_SetReference(int stratum,
     update_fb_drifts(abs_freq_ppm, update_interval);
   }
 
-  last_ref_update = *ref_time;
+  last_ref_update = now;
   last_ref_update_interval = update_interval;
 
   /* And now set the freq and offset to zero */