Bluetooth: Enable system processes to set bluetooth properties

ANT and BT is part of the same wcnsss subsystem and hence libbt-vendor
is being used by both ANT and BT stack for hardware initialization.
ANT stack runs in system permission which loads libbt-vendor which in turn
needs write access to bluetooth. properties.

Change-Id: I29a9b74504f1c03b98db3cddb2a53399f4b6115b