l2cap: Fix for REF responds with same DCIDs for different connections from IUT

Stack Not initiating L2CAP Disconnect when REF responds with same DCIDs for different connections from IUT
If a device receives a L2CAP_CREDIT_BASED_CONNECTION_RSP packet with an already assigned Destination CID,
 then both the original channel and the new channel shall be immediately discarded and not used.
Test: Verified with L2CAP/ECFC/BV-29-C

Change-Id: I75a67d6a7934c2015784c4471f86a4a5c54d9f67