Bluetooth: mgmt: Centralize message length checks

Bluetooth: mgmt: Centralize message length checks

This patch moves the command length information into the command handler
table allowing the removal of length checks from the handler functions
and doing the check in a single place before calling the handler
function.

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