mgcp_client: add function to generate e1-endpoint names

mgcp_client.h offers functions to generate endpoint names for wildcarded
request. This is used in osmo-bsc, lets now also add a function that can
generate e1-endpoint names.

Change-Id: Iec35b5bae8a7b07ddb3559f7114a24dcd10e8f14
Related: OS#2547
diff --git a/tests/mgcp_client/mgcp_client_test.err b/tests/mgcp_client/mgcp_client_test.err
index fbcf8f6..e114f79 100644
--- a/tests/mgcp_client/mgcp_client_test.err
+++ b/tests/mgcp_client/mgcp_client_test.err
@@ -72,4 +72,9 @@
 DLMGCP ptmap contains illegal mapping: codec=0 maps to pt=100
 DLMGCP ptmap contains illegal mapping: codec=113 maps to pt=2
 DLMGCP ptmap contains illegal mapping: codec=0 maps to pt=100
+DLMGCP MGCP client: using endpoint domain '@mgw'
+DLMGCP Cannot compose MGCP e1-endpoint name (ds/e1-15/s-1/su128-0@mgw), rate(128)/offset(0) combination is invalid!
+DLMGCP Cannot compose MGCP e1-endpoint name (ds/e1-15/s-1/su8-16@mgw), rate(8)/offset(16) combination is invalid!
+DLMGCP Cannot compose MGCP e1-endpoint name (ds/e1-15/s-0/su8-2@mgw), E1-timeslot number (0) is invalid!
+DLMGCP Cannot compose MGCP e1-endpoint name (ds/e1-15/s-64/su8-2@mgw), E1-timeslot number (64) is invalid!
 Done