MINOR: stats: report a "waiting" flags for sessions

This flag indicates if the session is still waiting for some memory.
diff --git a/src/dumpstats.c b/src/dumpstats.c
index a5c73fa..1abc7a9 100644
--- a/src/dumpstats.c
+++ b/src/dumpstats.c
@@ -5119,9 +5119,9 @@
 			     human_time(now.tv_sec - sess->logs.accept_date.tv_sec, 1));
 
 		chunk_appendf(&trash,
-			     "  txn=%p flags=0x%x meth=%d status=%d req.st=%s rsp.st=%s\n",
+			     "  txn=%p flags=0x%x meth=%d status=%d req.st=%s rsp.st=%s waiting=%d\n",
 			     &sess->txn, sess->txn.flags, sess->txn.meth, sess->txn.status,
-			     http_msg_state_str(sess->txn.req.msg_state), http_msg_state_str(sess->txn.rsp.msg_state));
+			      http_msg_state_str(sess->txn.req.msg_state), http_msg_state_str(sess->txn.rsp.msg_state), !LIST_ISEMPTY(&sess->buffer_wait));
 
 		chunk_appendf(&trash,
 			     "  si[0]=%p (state=%s flags=0x%02x endp0=%s:%p exp=%s, et=0x%03x)\n",