Bluetooth: Add le16 macro to Retransmission and Monitor Timeouts values

Fix a possible problem with Big Endian machines.

Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>
Reviewed-by: João Paulo Rechi Vita <jprvita@profusion.mobi>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>