Bluetooth: Add hci_conn_hash_lookup_le() helper function

Many of the existing LE connection lookups are forced to use
hci_conn_hash_lookup_ba() which doesn't take into account the address
type. What's worse, most of the users don't bother checking that the
returned address type matches what was wanted.

This patch adds a new helper API to look up LE connections based on
their address and address type, paving the way to have the
hci_conn_hash_lookup_ba() users converted to do more precise lookups.

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