df: add rootfs to is_dummy_filesystem

Author: ChrisDryden

src/uucore/src/lib/features/fsext.rs

@@ -393,6 +393,8 @@ fn is_dummy_filesystem(fs_type: &str, mount_option: &str) -> bool {
         | "kernfs"
         // for Irix 6.5
         | "ignore"
+        // Linux initial root filesystem
+        | "rootfs"
         // Binary format support pseudo-filesystem
         | "binfmt_misc" => true,
         _ => fs_type == "none"