Bluetooth: Add store_hint parameter to mgmt_new_key

Even for keys that shouldn't be stored some use cases require the
knowledge of a new key having been created so that the conclusion of a
successful pairing can be made. Therefore, always send the mgmt_new_key
event but add a store_hint parameter to it to indicate to user space
whether the key should be stored or not.

Signed-off-by: Johan Hedberg <johan.hedberg@nokia.com>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>