ext4: add module aliases for ext2 and ext3

Add module aliases for ext2 and ext3 when CONFIG_EXT4_USE_FOR_EXT23 is
set.  This makes the existing user-space stuff like mkinitrd working
as is.
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

fs/ext4/super.c

@@ -4005,6 +4005,7 @@ static inline void unregister_as_ext2(void)
 {
 	unregister_filesystem(&ext2_fs_type);
 }
+MODULE_ALIAS("ext2");
 #else
 static inline void register_as_ext2(void) { }
 static inline void unregister_as_ext2(void) { }
@@ -4031,6 +4032,7 @@ static inline void unregister_as_ext3(void)
 {
 	unregister_filesystem(&ext3_fs_type);
 }
+MODULE_ALIAS("ext3");
 #else
 static inline void register_as_ext3(void) { }
 static inline void unregister_as_ext3(void) { }