Bluetooth: Locking refactor in hci_le_conn_complete_evt

This patch moves hci_dev_lock and hci_dev_unlock calls to where they
are really required, reducing the critical region in hci_le_conn_
complete_evt function. hdev->lock is required only in hci_conn_del
and hci_conn_add call to protect concurrent add and remove operations
in hci_conn_hash list.

Signed-off-by: Andre Guedes <andre.guedes@openbossa.org>