alsa: Fix IEC958 digital output not unmuted on path activation

When selecting an HDMI/DisplayPort (IEC958) output path, the hardware
mute switch remains in kernel default state (muted), causing no audio
output despite correct software routing.

Root cause: pa_alsa_path_select() only sets mute switches when
mute_during_activation is enabled. No mixer paths enable this setting,
making the switch configuration code unreachable for IEC958 paths.

Solution: Always set mute switches to match device mute status after
path activation, regardless of mute_during_activation setting.

Testing: Added test-alsa-path-select tool to verify the fix.
- Loads mixer path and calls pa_alsa_path_select()
- Verifies switch states match expected values
- Tested on AMD Radeon HDMI and Realtek ALC257 analog

Manual verification:
- Before: IEC958 switch OFF, no audio
- After: IEC958 switch set correctly, audio works

This bug was inherited from PulseAudio's ALSA mixer path code where
HDMI path configurations lack IEC958 unmute sections.

Fixes: https://gitlab.freedesktop.org/pipewire/pipewire/-/issues/3261
See-Also: https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/issues/562
See-Also: 33be660e4b
See-Also: https://bugs.launchpad.net/hundredpapercuts/+bug/681996

spa/plugins/alsa/acp/meson.build

@@ -20,3 +20,12 @@ acp_lib = static_library(
   dependencies : [ spa_dep, alsa_dep, mathlib, ]
   )
 acp_dep = declare_dependency(link_with: acp_lib)
+
+executable('test-alsa-path-select',
+  [ 'test-alsa-path-select.c' ],
+  c_args : acp_c_args,
+  include_directories : [configinc, includes_inc ],
+  dependencies : [ spa_dep, alsa_dep, mathlib, ],
+  link_with : [ acp_lib ],
+  install : false,
+)