/lib/udev/rules.d/90-alsa-restore.rules is in alsa-utils 1.1.3-1ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 | ACTION=="add", SUBSYSTEM=="sound", KERNEL=="controlC*", KERNELS!="card*", TEST=="/usr/sbin", TEST=="/usr/share/alsa", GOTO="alsa_restore_go"
GOTO="alsa_restore_end"
LABEL="alsa_restore_go"
TEST!="/etc/alsa/state-daemon.conf", TEST=="/usr/sbin/alsactl", RUN+="/usr/sbin/alsactl -E HOME=/run/alsa restore $attr{device/number}"
TEST=="/etc/alsa/state-daemon.conf", TEST=="/usr/sbin/alsactl", RUN+="/usr/sbin/alsactl -E HOME=/run/alsa nrestore $attr{device/number}"
LABEL="alsa_restore_end"
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