Changes

trau_frame: fix de/encoding of HR-data-8k frames

Functions for decoding and encoding HR-data TRAU frames in 8 kbit/s
submultiplexing, accessible via osmo_trau_frame_encode() and
osmo_trau_frame_decode_8k() public APIs, were broken: movement
of data bits was wrong, and in the encoding direction the setting
of the last sync bit was missed.

Change-Id: I051b0b70adffcc473dcbb42a555c19088973cc90