xfs_repair: validate & fix inode CRCs

xfs_repair: validate & fix inode CRCs

xfs_repair doesn't ever check an inode's CRC, so it never repairs
them.  If the root inode or realtime inodes have bad crcs, the
fs won't even mount and can't be fixed (without using xfs_db).

It's fairly straightforward to just test the inode CRC before
we do any other checking or modification of the inode, and
just mark it dirty if it's wrong and needs to be re-written.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>