[bluez] Fix bluetoothd startup dbus crash. Fixes JB#11740

When phone startup with bluetooth disabled, some times because of
the rfkill initialize sequence, the hci will up then down quickly.
In this case, the dbus_connection_remove_filter() will be called
twice because of the nested call of
filter_data_free() and filter_data_remove_callback().
Add a flag to make sure dbus_connection_remove_filter() won't be
called twice.