Bluetooth: Fix incorrect removing of IRKs

The commit cad20c27 was supposed to
fix handling of devices first using public addresses and then
switching to RPAs after pairing. Unfortunately it missed a couple of
key places in the code.

1. When evaluating which devices should be removed from the existing
white list we also need to consider whether we have an IRK for them or
not, i.e. a call to hci_find_irk_by_addr() is needed.

2. In smp_notify_keys() we should not be requiring the knowledge of
the RPA, but should simply keep the IRK around if the other conditions
require it.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Cc: stable@vger.kernel.org # 4.4+