Fix for LASSERT failure in ll_inode_getattr.

Fix for LASSERT failure in ll_inode_getattr.
Also removes get_info("brw_size") and instead uses o_blksize from the OSC
  to set the "optimum" block size for IO (ala st_blksize from fstat).  We
  do not yet pass this from the OST to the client, but we should as soon
  as BA OSTs do.
This also removes a problem where we returned bad values for st_blksize at
  times (4096 when the inode was created, 65536 * num_osts later, instead
  of 65536 * num_stripes).