Introduce log fmt helpers LOGPENDP and LOGPCONN

Let's define macro once and use it everywhere instead of passing endp
information in different ways everywhere. Furthermore, use conn whenever
appropiate to have more information.

Change-Id: I1c49b1eb16bc5f1010376da5cf407ca6e31d81f2
diff --git a/src/libosmo-mgcp/mgcp_endp.c b/src/libosmo-mgcp/mgcp_endp.c
index fa2dd28..eec46bf 100644
--- a/src/libosmo-mgcp/mgcp_endp.c
+++ b/src/libosmo-mgcp/mgcp_endp.c
@@ -36,8 +36,7 @@
  *  \param[in] endp endpoint to release */
 void mgcp_endp_release(struct mgcp_endpoint *endp)
 {
-	LOGP(DLMGCP, LOGL_DEBUG, "Releasing endpoint:0x%x\n",
-	     ENDPOINT_NUMBER(endp));
+	LOGPENDP(endp, DLMGCP, LOGL_DEBUG, "Releasing endpoint\n");
 
 	/* Normally this function should only be called when
 	 * all connections have been removed already. In case