Bluetooth: Fix rejecting SMP security request in slave role

The SMP security request is for a slave role device to request the
master role device to initiate a pairing request. If we receive this
command while we're in the slave role we should reject it appropriately.

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