add a stats counter for clients dropped due to recursive-clients limit

(cherry picked from commit 715afa9c57)

bin/named/statschannel.c

@@ -317,6 +317,9 @@ init_desc(void) {
 		       "QryUsedStale");
 	SET_NSSTATDESC(prefetch, "queries triggered prefetch", "Prefetch");
 	SET_NSSTATDESC(keytagopt, "Keytag option received", "KeyTagOpt");
+	SET_NSSTATDESC(reclimitdropped,
+		       "queries dropped due to recursive client limit",
+		       "RecLimitDropped");
 
 	INSIST(i == ns_statscounter_max);
 

bin/tests/system/fetchlimit/tests.sh

@@ -179,5 +179,17 @@ echo_i "clients count exceeded 380 on $exceeded trials (expected 0)"
 if [ $ret != 0 ]; then echo_i "failed"; fi
 status=`expr $status + $ret`
 
+echo_i "checking drop statistics"
+rm -f ns3/named.stats
+$RNDCCMD stats
+for try in 1 2 3 4 5; do
+    [ -f ns3/named.stats ] && break
+    sleep 1
+done
+drops=`grep 'queries dropped due to recursive client limit' ns3/named.stats | sed 's/\([0-9][0-9]*\) queries.*/\1/'`
+[ "${drops:-0}" -ne 0 ] || ret=1
+if [ $ret != 0 ]; then echo_i "failed"; fi
+status=`expr $status + $ret`
+
 echo_i "exit status: $status"
 [ $status -eq 0 ] || exit 1