LU-80 ldiskfs: large EA support

LU-80 ldiskfs: large EA support

This patch implements the large EA support in ext4. If the size of
an EA value is larger than the blocksize, then the EA value would
not be saved in the external EA block, instead it would be saved
in an external EA inode. So, the patch also helps support a larger
number of EAs.

Signed-off-by: James Simmons <uja.ornl@gmail.com>
Change-Id: Ic08921cf13483c9b28560c987773d7aa36c62fac
Reviewed-on: http://review.whamcloud.com/1708
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>