Bluetooth: Fix ignoring unknown SMP authentication requirement bits

The SMP specification states that we should ignore any unknown bits from
the authentication requirement. We already have a define for masking out
unknown bits but we haven't used it in all places so far. This patch
adds usage of the AUTH_REQ_MASK to all places that need it and ensures
that we don't pass unknown bits onward to other functions.

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