mgcp_protocol: refactor function create_response_with_sdp

The function create_response_with_sdp calls add_params, which is rather short.
The code in there can also be put in create_response_with_sdp. The
decision whether the endpoint name (Z) should be added or not, should be
made by the caller.

Change-Id: I7e29c513f4386832646e96194ed6c2397405ed3b
Related: SYS#5535
1 file changed