shared/shell: Set NON_INTERACTIVE env

This sets NON_INTERACTIVE environment variable which applications can
then use to query under what mode they are running.
diff --git a/src/shared/shell.c b/src/shared/shell.c
index 0f6d613..85657c2 100644
--- a/src/shared/shell.c
+++ b/src/shared/shell.c
@@ -818,6 +818,9 @@
 	data.argv = argv + optind;
 	data.mode = (data.argc > 0);
 
+	if (data.mode)
+		bt_shell_set_env("NON_INTERACTIVE", &data.mode);
+
 	main_loop = g_main_loop_new(NULL, FALSE);
 
 	rl_init();