Bluetooth: Save remote L2CAP fixed channel mask

Fixed channel mask needs to be stored to decide whether to
use A2MP for example. So far save only one relevant byte which
keeps all information we need.

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