ntp: delay initial transmission until first resolving ends

This will be needed to prevent loading of dump files after sources have
already accumulated samples and possibly reference was already updated
when async resolving of sources is implemented.

main.c

@@ -147,6 +147,8 @@ post_init_ntp_hook(void *anything)
 
   RTC_StartMeasurements();
   RCL_StartRefclocks();
+  NSR_StartSources();
+  NSR_AutoStartSources();
 
   /* Special modes can end only when sources update their reachability.
      Give up immediatelly if there are no active sources. */
@@ -184,6 +186,7 @@ post_init_rtc_hook(void *anything)
 {
   if (CNF_GetInitSources() > 0) {
     CNF_AddInitSources();
+    NSR_StartSources();
     assert(REF_GetMode() != REF_ModeNormal);
     /* Wait for mode end notification */
   } else {