Add DoT support to bind

Parse the configuration of tls objects into SSL_CTX* objects.  Listen on
DoT if 'tls' option is setup in listen-on directive.  Use DoT/DoH ports
for DoT/DoH.

lib/isc/netmgr/tcpdns.c

@@ -471,6 +471,7 @@ isc__nm_async_tcpdnsstop(isc__networker_t *worker, isc__netievent_t *ev0) {
 			break;
 		default:
 			INSIST(0);
+			ISC_UNREACHABLE();
 		}
 		isc__nmsocket_detach(&sock->outer);
 	}