Bluetooth: HCI: Fix updating RPA too early

Checking work pending flag does not account the delay before the work is
submitted so this make use a flag to track when the RPA is valid.

Change-Id: I2d858e5163455ce90eb6273c6a8824c5c6d44ae1
Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>