Bluetooth: Use LE buffers for LE traffic

Bluetooth chips may have separate buffers for LE traffic.
This patch add support to use LE buffers provided by the chip.

Signed-off-by: Ville Tervo <ville.tervo@nokia.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>