Bluetooth: Add basic LE SC OOB support for remote OOB data

This patch adds basic OOB pairing support when we've received the remote
OOB data. This includes tracking the remote r value (in smp->rr) as well
as doing the appropriate f4() call when needed. Previously the OOB rand
would have been stored in smp->rrnd however these are actually two
independent values so we need separate variables for them. Na/Nb in the
spec maps to smp->prnd/rrnd and ra/rb maps to smp->rr with smp->pr to
come once local OOB data is supported.

Signed-off-by: Johan Hedberg <johan.hedberg@intel.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>