touch ntp servers at most once every seconds

The delay between te first and second query was only the remainder of the current second. This is causing rate limiting issues on some server resulting in 'Offset unknown'
After this pull the delay between the first and second query is the remainder of the current second + 1.

plugins/check_ntp.c

@@ -430,6 +430,7 @@ double offset_request(const char *host, int *status){
 				if(verbose) printf("sending request to peer %d\n", i);
 				setup_request(&req[i]);
 				write(socklist[i], &req[i], sizeof(ntp_message));
+				if(servers[i].waiting == 0) now_time++;
 				servers[i].waiting=now_time;
 				one_written=1;
 				break;
@@ -461,7 +462,6 @@ double offset_request(const char *host, int *status){
 				servers[i].stratum=req[i].stratum;
 				servers[i].rtdisp=NTP32asDOUBLE(req[i].rtdisp);
 				servers[i].rtdelay=NTP32asDOUBLE(req[i].rtdelay);
-				servers[i].waiting=0;
 				servers[i].flags=req[i].flags;
 				servers_readable--;
 				one_read = 1;