MINOR: cli/activity: report the accept queue sizes in "show activity"

Seeing the size of each ring helps understand which threads are
overloaded and why some of them are less often elected than others
by the multi-queue load balancer.
diff --git a/src/cli.c b/src/cli.c
index 755a94c..5db1894 100644
--- a/src/cli.c
+++ b/src/cli.c
@@ -1071,6 +1071,7 @@
 	chunk_appendf(&trash, "\naccepted:");     for (thr = 0; thr < global.nbthread; thr++) chunk_appendf(&trash, " %u", activity[thr].accepted);
 	chunk_appendf(&trash, "\naccq_pushed:");  for (thr = 0; thr < global.nbthread; thr++) chunk_appendf(&trash, " %u", activity[thr].accq_pushed);
 	chunk_appendf(&trash, "\naccq_full:");    for (thr = 0; thr < global.nbthread; thr++) chunk_appendf(&trash, " %u", activity[thr].accq_full);
+	chunk_appendf(&trash, "\naccq_ring:");    for (thr = 0; thr < global.nbthread; thr++) chunk_appendf(&trash, " %u", (accept_queue_rings[thr].tail - accept_queue_rings[thr].head + ACCEPT_QUEUE_SIZE)%ACCEPT_QUEUE_SIZE);
 
 	chunk_appendf(&trash, "\n");