Fix HDLC DSP transmit (DL_DATA frames were bounced back upwards instead of
being sent down as PH_DATA frames)

Thanks to Andreas Eversberg for the fix!
Signed-off-by: NAndreas Eversberg <andreas@eversberg.eu>
Signed-off-by: NPeter Schlaile <root@asterisk.schlaile.de>
Signed-off-by: NKarsten Keil <kkeil@suse.de>