mgcp_client: error on too long conn id

Instead of just silently truncating the conn ID if it is too long, rather
verify its length and return an error where applicable.

Adjust expected test output.

Change-Id: If2a1aab1f13e771a6705c430e3c75bd42477a23b
diff --git a/tests/mgcp_client/mgcp_client_test.err b/tests/mgcp_client/mgcp_client_test.err
index 1d5a1a0..b20f93f 100644
--- a/tests/mgcp_client/mgcp_client_test.err
+++ b/tests/mgcp_client/mgcp_client_test.err
@@ -66,4 +66,6 @@
 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 Failed to parse MGCP response (parameter label: I): the received conn ID is too long: 39, maximum is 32 characters
+DLMGCP Cannot parse MGCP response (head parameters)
 Done