Bluetooth: Remove conn_unfinished variable from hci_connect_le()

The conn_unfinished variable makes the entire logic of
hci_connect_le() rather confusing. By restructuring and clarifying the
logic we can actually remove the conn_unfinished variable and still
keep the same behavior.

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