Bluetooth: Fix sending a HCI Authorization Request over LE links

In the case that the link is already in the connected state and a
Pairing request arrives from the mgmt interface, hci_conn_security()
would be called but it was not considering LE links.

Reported-by: João Paulo Rechi Vita <jprvita@openbossa.org>
Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@openbossa.org>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>