Bluetooth: Use shorter "rand" name for "randomizer"

The common short form of "randomizer" is "rand" in many places
(including the Bluetooth specification). The shorter version also makes
for easier to read code with less forced line breaks. This patch renames
all occurences of "randomizer" to "rand" in the Bluetooth subsystem
code.

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