streams: Named systemd sockets are only supported since systemd v227

configure.ac

@@ -1002,6 +1002,10 @@ if test x$systemd = xtrue; then
 		 AC_SUBST(systemd_journal_CFLAGS)
 		 AC_SUBST(systemd_journal_LIBS)]
 	)
+	saved_LIBS=$LIBS
+	LIBS="$systemd_LIBS $systemd_daemon_LIBS"
+	AC_CHECK_FUNCS(sd_listen_fds_with_names)
+	LIBS=$saved_LIBS
 fi
 
 if test x$tss_trousers = xtrue; then

src/libstrongswan/networking/streams/stream_service_systemd.c

@@ -29,6 +29,11 @@
  */
 stream_service_t *stream_service_create_systemd(char *uri, int backlog)
 {
+#ifndef HAVE_SD_LISTEN_FDS_WITH_NAMES
+	DBG1(DBG_NET, "unable to open stream URI '%s': named systemd sockets not "
+		 "supported", uri);
+	return NULL;
+#else
 	int i, num_fds, fd;
 	char **fdmap;
 
@@ -62,4 +67,5 @@ stream_service_t *stream_service_create_systemd(char *uri, int backlog)
 		return NULL;
 	}
 	return stream_service_create_from_fd(fd);
+#endif
 }