e2fsck: make sure system.data xattr is present

e2fsck: make sure system.data xattr is present

E2fsprogs used to assume that if i_size is less than 60 bytes, the
system.data xattr isn't needed (and should be removed).  The kernel
disagree, and will declare the file system to be corrupted.  Enforce
the tighter constraints assumed by the kernel.

Signed-off-by: Theodore Ts'o <tytso@mit.edu>