Bluetooth: L2CAP: Mark finishing CoC configuration on BR/EDR

When each side involved in getting configured L2CAP CoC channel on
BR/EDR transport aggrees on configuration contract regarding in/out MTU,
set proper context flags to start prepare finalize config process.

Change-Id: Ic821ea3b961442be758ad4e2d91b2d812e2a54b5
Signed-off-by: Arkadiusz Lichwa <arkadiusz.lichwa@tieto.com>