topology_hiding: fix encoded Contact length calculation

This leads to segfaults (and probable vulnerabilities) when the allocated buffer
is not long enough to contain its contents.

This bug was introduced in
e23be5d
presumably as a copy-and-paste mistake.

modules/topology_hiding/topo_hiding_logic.c

@@ -1618,7 +1618,7 @@ static char* build_encoded_contact_suffix(struct sip_msg* msg,int *suffix_len)
 					/* we just iterate over the unknown params */
 					for (i=0;i<ctu.u_params_no;i++) {
 						if (str_match(&el->param_name, &ctu.u_name[i]))
-							suffix_len += topo_ct_param_len(&ctu.u_name[i], &ctu.u_val[i], 0);
+							total_len += topo_ct_param_len(&ctu.u_name[i], &ctu.u_val[i], 0);
 					}
 				}
 			}
@@ -1634,7 +1634,7 @@ static char* build_encoded_contact_suffix(struct sip_msg* msg,int *suffix_len)
 			for (el=th_hdr_param_list;el;el=el->next) {
 				for (it=((contact_body_t *)msg->contact->parsed)->contacts->params;it;it=it->next) {
 					if (str_match(&el->param_name, &it->name))
-						suffix_len += topo_ct_param_len(&it->name, &it->body, 1);
+						total_len += topo_ct_param_len(&it->name, &it->body, 1);
 				}
 			}
 		}