Add retry mechnism for setting BT MAC addr

This replaces 3bfb183f with a retry mechanism, where the BT mac is
(re)tried every 1 second for up to 5 seconds (configurable).

If this doesn't play nicely with udev rules when using RUN, BT_TIMEOUT
can be set in the env.

bootmac

@@ -16,6 +16,7 @@ WLAN_INTERFACE="wlan0"
 BT_INTERFACE="hci0"
 # Default MAC prefix
 MAC_PREFIX="0200"
+BT_TIMEOUT=${BT_TIMEOUT:-5} # seconds
 
 log() {
     echo "$@" | logger -t "bootmac"
@@ -141,9 +142,6 @@ mac_generate() {
 }
 
 mac_bluetooth() {
-    # Some Bluetooth adapters take time before they can be configured
-    sleep 1
-
     log "setting Bluetooth MAC to $BT_MAC"
 
     # Check if the Bluetooth interface is up
@@ -162,7 +160,24 @@ mac_bluetooth() {
     # The 'yes | btmgmt xxx' workaround is needed for proper working of btmgmt
     # as noted in https://gitlab.com/postmarketOS/bootmac/-/issues/3
     yes | btmgmt -i "$BT_INTERFACE" power off
-    yes | btmgmt -i "$BT_INTERFACE" public-addr "$BT_MAC"
+
+    # Setting the mac addr might fail if the device/driver hasn't finished
+    # initializing, so retry
+    timeout=0
+    while [ $timeout -lt "$BT_TIMEOUT" ]; do
+        if yes | btmgmt -i "$BT_INTERFACE" public-addr "$BT_MAC"; then
+            break
+        fi
+        echo "Unable to set Bluetooth MAC, retrying after 1 second..."
+        sleep 1
+        timeout=$((timeout + 1))
+    done
+
+    if [ $timeout -ge "$BT_TIMEOUT" ]; then
+        echo "Failed to set Bluetooth MAC address, command timed out after $BT_TIMEOUT seconds"
+        return 1
+    fi
+
     if [ -n "$BT_RFKILL_UNBLOCKED" ]; then
         log "restoring Bluetooth rfkill state to unblocked"
         rfkill unblock bluetooth