mgcp_network: use mgcp_rtp_codec in downlink format callback

The callback function mgcp_get_format() is used to request the codec
parameters for a specific connection. This function returns the
parameters as idividual pointers. Since there is a struct that holds all
important codec information among the ones which are currently returned
by mgcp_get_format, lets just use this codec struct as single return
value.

Change-Id: I348f9141eb59ed1a986447b96ab4a24ddf326936
Related: OS#3807
diff --git a/include/osmocom/mgcp/mgcp_internal.h b/include/osmocom/mgcp/mgcp_internal.h
index a6239c2..35b535a 100644
--- a/include/osmocom/mgcp/mgcp_internal.h
+++ b/include/osmocom/mgcp/mgcp_internal.h
@@ -298,9 +298,8 @@
 				      struct mgcp_conn_rtp *conn_src);
 
 void mgcp_get_net_downlink_format_default(struct mgcp_endpoint *endp,
-					  int *payload_type,
-					  const char**audio_name,
-					  const char**fmtp_extra,
+					  const struct mgcp_rtp_codec **codec,
+					  const char **fmtp_extra,
 					  struct mgcp_conn_rtp *conn);
 
 /* internal RTP Annex A counting */