ext4: enable quota enforcement based on mount options

When quota information is stored in quota files, we enable only quota
accounting on mount and enforcement is enabled only in response to
Q_QUOTAON quotactl. To make ext4 behavior consistent with XFS, we add a
possibility to enable quota enforcement on mount by specifying
corresponding quota mount option (usrquota, grpquota, prjquota).

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