mux from not-started raw TS: fill with 0xFF

When the channelized mux reads from a raw TS, but that raw TS is
not in tx_started state yet, the read function returns "fake" data.
However, it was actually returning uninitialized memory content,
rather than 0xFF filler used everywhere else, thereby transmitting
uninit-memory garbage to whatever is connected to the E1 line.
Change it to fill with 0xFF, same as the filler used in other cases
such as inactive timeslots.

Change-Id: I42849a6d19b020bab789853c3b60af6a1c09f92f
---
M src/mux_demux.c
1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/src/mux_demux.c b/src/mux_demux.c
index a0ae717..72379fe 100644
--- a/src/mux_demux.c
+++ b/src/mux_demux.c
@@ -55,8 +55,10 @@
 
 	/* If we're not started yet, we 'fake' data until the other side
 	 * send something */
-	if (l < 0 && errno == EAGAIN && !ts->raw.tx_started)
+	if (l < 0 && errno == EAGAIN && !ts->raw.tx_started) {
+		memset(buf, 0xFF, len);
 		return len;
+	}
 
 	ts->raw.tx_started = true;
 

