raspbiantools: pin Bluez to the RP repos for Buster

Upgrading via 'apt' the Bluez package with a the version from Debian updates will overwrite the RP package. This breaks pairing for some gamepads, thus try to always have installed the RP package.
Pin the package so it's always installed/updated from archive.raspberrypi.org on RaspiOS 10 'Buster'.

Added a related change to how 'apt' is run when updating from `raspbiantoolsz:
 * add '--allow-downgrades' to make sure that 'bluez' is retrieved from the RP repos if it was already upgraded by an upstream update.

Author: cmitu

scriptmodules/supplementary/raspbiantools.sh

@@ -18,8 +18,11 @@ function apt_upgrade_raspbiantools() {
     # install an older kernel/firmware for stretch to resolve newer kernel issues or unhold if updating to a newer release
     stretch_fix_raspbiantools
 
+    # on Buster, always install the Bluez package from the RPI repos
+    buster_bluez_pin_raspbiantools
+
     aptUpdate
-    apt-get -y dist-upgrade
+    apt-get -y dist-upgrade --allow-downgrades
 }
 
 function lxde_raspbiantools() {
@@ -73,6 +76,19 @@ function stretch_fix_raspbiantools() {
     fi
 }
 
+function buster_bluez_pin_raspbiantools() {
+    # pin the 'bluez' package to the RPI repos to prevent any Debian updates overwriting it
+    # use Priority 1001 to force the the installation even when the Debian package is installed
+    local pin_file="/etc/apt/preferences.d/01-bluez-pin"
+    if isPlatform "rpi" && [[ "$__os_debian_ver" -eq 10 && ! -f "$pin_file" ]] ; then
+        cat << PIN_EOF > "$pin_file"
+Package: bluez
+Pin: origin archive.raspberrypi.org
+Pin-Priority: 1001
+PIN_EOF
+    fi
+}
+
 function install_firmware_raspbiantools() {
     local ver="$1"
     local state="$2"