fdkaacenc: Add missing SURROUND mappings
SURROUND is more to spec according to the FIXME comments, so add this.
Also add SIDE for 5 and 5.1 because of ffmpeg compatibility, because the following pipeline downmixes to mono otherwise:
gst-launch-1.0 audiotestsrc num-buffers=1 ! audio/x-raw, channels=6 ! avenc_ac3 ! avdec_ac3 ! audioconvert ! fdkaacenc ! fakesink -v
Fixes #1327 (closed)
Edited by Jan Alexander Steffens