When decoding files, their audio is rematrixed to mono or stereo
depending on the negotiated format. Libswresample does not support
rematrixing from Dolby Surround 5.1, so skip over streams with this
layout. If the file only contains Dolby 5.1, switch back to default
audio input device.

Change-Id: I526e3c9b2ec92794818e74f8c369a8c8f3c41b27