af_lavrresample: fix inverted condition

This was added with the previous commit. It likely broke some obscure
special-cases, which (hopefully) do not happen with normal playback.
audio: fix ALSA 4 channel surround output

It turns out that ALSA's 4 channel layout is different from mpv's and
ffmpeg's 4.0 layout. Thus trying to do 4 channel output led to incorrect
remixing via lib{av,sw}resample.

Fix the default layouts for the internal filter chain as well, although
I'm not sure if it matters at all.
Merge remote-tracking branch 'remotes/origin/master' into lua_experiment