LU-11074 mdc: set correct body eadatasize for getxattr()

In mdc_intent_getxattr_pack() set mbo_eadatasize to the size of the
xattr values buffer rather than the size of the xattr names buffer.

Signed-off-by: John L. Hammond <jhammond@whamcloud.com>
Change-Id: Ibbed6aba6718f50eed1a08d506d526b1e0e042c8
Reviewed-on: https://review.whamcloud.com/32739


Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andrew Perepechko <c17827@cray.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Tested-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>