Bluetooth: Fix 6loWPAN peer lookup

This patch fixes peer address lookup for 6loWPAN over Bluetooth Low
Energy links.

ADDR_LE_DEV_PUBLIC, and ADDR_LE_DEV_RANDOM are the values allowed for
"dst_type" field in the hci_conn struct for LE links.

Signed-off-by: Claudio Takahasi <claudio.takahasi@openbossa.org>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>