Split the enable-lfe-remixing setting into two

remixing-produce-lfe controls upmixing, and remixing-consume-lfe
controls downmixing. The motivation is that a user might want to
synthesize LFE while playing stereo audio on his/her 5.1 speakers,
but at the same time follow the industry recommendation to omit
the LFE channel when producting a stereo downmix (e.g. for headphones)
from 5.1 content. Or the other way round.

Fixes: #753.

src/daemon/daemon-conf.h

@@ -70,7 +70,8 @@ typedef struct pa_daemon_conf {
         avoid_resampling,
         disable_remixing,
         remixing_use_all_sink_channels,
-        disable_lfe_remixing,
+        remixing_produce_lfe,
+        remixing_consume_lfe,
         load_default_script_file,
         disallow_exit,
         log_meta,