L2CAP: Fix wrong CID on reject

[zxzxwu]

It looks like a typo because on success it takes

    def on_connection_request(self, request: L2CAP_Connection_Request) -> None:
        self.destination_cid = request.source_cid
        self._change_state(self.State.WAIT_CONNECT)
        self.send_control_frame(
            L2CAP_Connection_Response(
                identifier=request.identifier,
                destination_cid=self.source_cid,
                source_cid=self.destination_cid,
                result=L2CAP_Connection_Response.Result.CONNECTION_SUCCESSFUL,
                status=0x0000,
            )
        )


    def on_l2cap_connection_request(
        self, connection: Connection, cid: int, request: L2CAP_Connection_Request
    ) -> None:
            ...
            source_cid = self.find_free_br_edr_cid(connection_channels)
            ...
            channel = ClassicChannel(
                manager=self,
                connection=connection,
                signaling_cid=cid,
                psm=request.psm,
                source_cid=source_cid,
                spec=server.spec,
            )

[barbibulle]

You're right, this was reversed. In practice, it shouldn't have cause problems, because the spec says that for an unsuccessful result, those fields shall be ignored:
" If the result field does not indicate the connection was
successful, the DCID and SCID fields may be invalid and shall be ignored."

But it's good to fix it anyway.

[zxzxwu]

This could help initiator to identify which L2CAP_CONNECTION_REQ is rejected, yet it's likely an ambiguous case, since L2CAP TS doesn't provide any TC about rejected response.