MEDIUM: connection: merge the send_wait and recv_wait entries

In practice all callers use the same wait_event notification for any I/O
so instead of keeping specific code to handle them separately, let's merge
them and it will allow us to create new events later.
diff --git a/include/proto/connection.h b/include/proto/connection.h
index dd37822..7e6e203 100644
--- a/include/proto/connection.h
+++ b/include/proto/connection.h
@@ -403,8 +403,7 @@
 	conn->proxy_netns = NULL;
 	LIST_INIT(&conn->list);
 	LIST_INIT(&conn->session_list);
-	conn->send_wait = NULL;
-	conn->recv_wait = NULL;
+	conn->subs = NULL;
 	conn->idle_time = 0;
 	conn->src = NULL;
 	conn->dst = NULL;
@@ -530,15 +529,10 @@
 
 static inline void conn_force_unsubscribe(struct connection *conn)
 {
-	if (conn->recv_wait) {
-		conn->recv_wait->events &= ~SUB_RETRY_RECV;
-		conn->recv_wait = NULL;
-	}
-	if (conn->send_wait) {
-		conn->send_wait->events &= ~SUB_RETRY_SEND;
-		conn->send_wait = NULL;
-	}
-
+	if (!conn->subs)
+		return;
+	conn->subs->events = 0;
+	conn->subs = NULL;
 }
 
 /* Releases a connection previously allocated by conn_new() */