ext4: Set flags on quota files directly

Currently immutable and noatime flags on quota files are set by quota
code which requires us to copy inode->i_flags to our on disk version of
quota flags in GETFLAGS ioctl and ext4_do_update_inode(). Move to
setting / clearing these on-disk flags directly to save that copying.

Signed-off-by: Jan Kara <jack@suse.cz>