MINOR: quic: Implement qc_process_mux()

At this time, we only add calls to qc_resume_each_sending_qcs()
which handle the flow control and send lists.
diff --git a/src/mux_quic.c b/src/mux_quic.c
index 707769f..8d2473a 100644
--- a/src/mux_quic.c
+++ b/src/mux_quic.c
@@ -1272,9 +1272,16 @@
 static int qc_process_mux(struct qcc *qcc)
 {
 	TRACE_ENTER(QC_EV_QCC_WAKE, qcc->conn);
-	/* XXX TO DO XXX */
+
+	/* First we always process the flow control list because the streams
+	 * waiting there were already elected for immediate emission but were
+	 * blocked just on this.
+	 */
+	qc_resume_each_sending_qcs(qcc, &qcc->fctl_list);
+	qc_resume_each_sending_qcs(qcc, &qcc->send_list);
+
 	TRACE_LEAVE(QC_EV_QCC_WAKE, qcc->conn);
-	return 0;
+	return 1;
 }