client: eliminate destructive parameter parsing

The function mgcp_response_parse_params() that is used to parse the
SDP parameters edits the content of the r->body.

- Create a local copy of r->body and work on this copy to keep
  the original r-body in its original state.

Change-Id: Ia475036f7f3802b1638e0511a5e9162fea1592eb
1 file changed