e2fsck: ea_inode hash validation

e2fsck: ea_inode hash validation

In original implementation of ea_inode feature, each xattr inode had
a single parent. Child inode tracked the parent by storing its inode
number in i_mtime field. Also, child's i_generation matched parent's
i_generation.

With deduplication support, xattr inodes can now be shared so a single
backpointer is not sufficient to achieve strong binding. This is now
replaced by hash validation.

Signed-off-by: Tahsin Erdogan <tahsin@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>