Improve dnssec-timestamp-checking related logging behavior.

dnsmasq already logs (at startup)
  DNSSEC signature timestamps not checked until system time valid
if the system time is considered to be invalid.

Do also log the opposite case, i.e. if the time at startup is valid.

--- src/dnsmasq.c
+++ src/dnsmasq.c
@@ -885,6 +885,9 @@
       if (rc == 1)
 	my_syslog(LOG_INFO, _("DNSSEC signature timestamps not checked until system time valid"));
 
+      if (daemon->timestamp_file && rc == 0) /* daemon->back_to_the_future is probably an equivalent condition */
+        my_syslog(LOG_INFO, _("system time considered valid, checking DNSSEC signature timestamps."));
+
       for (ds = daemon->ds; ds; ds = ds->next)
 	my_syslog(LOG_INFO, _("configured with trust anchor for %s keytag %u"),
 		  ds->name[0] == 0 ? "<root>" : ds->name, ds->keytag);