Bluetooth: Find hci_conn by BT_CONNECT state

This patch changes hci_cs_le_create_conn to perform hci_conn lookup
by state instead of bdaddr.

Since we can have only one LE connection in BT_CONNECT state, we can
perform LE hci_conn lookup by state. This way, we don't rely on
hci_sent_cmd_data helper to find the hci_conn object.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>