Report when loading of dhparam-file fails

prior to this loading of the configuration could fail without
an informative error message being logged.

lib/ns/listenlist.c

@@ -22,6 +22,7 @@
 #include <dns/acl.h>
 
 #include <ns/listenlist.h>
+#include <ns/log.h>
 
 static void
 destroy(ns_listenlist_t *list);
@@ -116,6 +117,13 @@ listenelt_create(isc_mem_t *mctx, in_port_t port, dns_acl_t *acl,
 				if (!isc_tlsctx_load_dhparams(
 					    sslctx, tls_params->dhparam_file))
 				{
+					isc_log_write(ns_lctx,
+						      NS_LOGCATEGORY_GENERAL,
+						      NS_LOGMODULE_INTERFACEMGR,
+						      ISC_LOG_ERROR,
+						      "loading of dhparam-file "
+						      "'%s' failed",
+						      tls_params->dhparam_file);
 					result = ISC_R_FAILURE;
 					goto tls_error;
 				}