bluetooth: Provide (HSP/HFP-received) battery level as device property

Part-of: <https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/merge_requests/482>

src/modules/bluetooth/backend-native.c

@@ -769,6 +769,7 @@ static void rfcomm_io_callback(pa_mainloop_api *io, pa_io_event *e, int fd, pa_i
                 switch (key) {
                     case 1:
                         pa_log_notice("Battery Level: %d0%%", val + 1);
+                        pa_bluetooth_device_report_battery_level(t->device, (val + 1) * 10);
                         break;
                     case 2:
                         pa_log_notice("Dock Status: %s", val ? "docked" : "undocked");