Bluetooth: Remove pointless bdaddr_to_le() helper function

The bdaddr_to_le() function tries to convert the internal address
type to one that matches the HCI address type for LE. It does not
handle any address types not used by LE and in the end just make
the code a lot harder to read.

So instead of just hiding behind a magic function, just convert
the internal address type where it needs to be converted. And it
turns out that these are only two cases anyway. One when creating
new LE connections and the other when loading the long term keys.
In both cases this makes it more clear on what it going on.

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