LU-13077 pfl: cleanup xattr checking

LU-13077 pfl: cleanup xattr checking

Cleanup xattr checking in mdd and lod layers for PFL.

Reported-by: Clement Barthelemy <clement.barthelemy@nextino.eu>
Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: I2841b615ee304785fbf316b829d8280eefc3878a
Reviewed-on: https://review.whamcloud.com/37010
Reviewed-by: Olaf Faaland-LLNL <faaland1@llnl.gov>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>