ext4: add EXT4_JOURNAL_DATA_FL and EXT4_EXTENTS_FL to modifiable mask

Add EXT4_JOURNAL_DATA_FL and EXT4_EXTENTS_FL to EXT4_FL_USER_MODIFIABLE
to recognize that they are modifiable by userspace. So far we got away
without having them there because ext4_ioctl_setflags() treats them in a
special way. But it was really confusing like that.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>