Bluetooth: Host: Use RPA as responder address if BT_PRIVACY=y

When a PAwR sync connects to a PAwR advertiser and CONFIG_BT_PRIVACY
is enabled a Resolvable Private Address will be used. Use that
as responder address instead of the identity address to match what
the central sees.

Signed-off-by: Herman Berget <herman.berget@nordicsemi.no>