Bluetooth: Fix regression with L2CAP configuration in Basic Mode

Basic Mode is the default mode of operation of a L2CAP entity. In
this case the RFC (Retransmission and Flow Control) configuration
option should not be used at all.

Normally remote L2CAP implementation should just ignore this option,
but it can cause various side effects with other Bluetooth stacks
that are not capable of handling unknown options.

Signed-off-by: Gustavo F. Padovan <gustavo@las.ic.unicamp.br>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>