BUG/MEDIUM: stream_interface: Call the wake callback after sending.

If we subscribed to send, and the callback is called, call the wake callback
after, so that process_stream() may be woken up if needed.

This is 1.9-specific, no backport is needed.
diff --git a/src/stream_interface.c b/src/stream_interface.c
index 52aa7c4..51f2300 100644
--- a/src/stream_interface.c
+++ b/src/stream_interface.c
@@ -764,8 +764,10 @@
 
 	if (!cs)
 		return NULL;
-	if (!(si->wait_list.wait_reason & SUB_CAN_SEND))
+	if (!(si->wait_list.wait_reason & SUB_CAN_SEND)) {
 		si_cs_send(cs);
+		si_cs_wake_cb(cs);
+	}
 	return (NULL);
 }