LU-11450 mdd: avoid logging trusted.som xattr in changelogs

LU-11450 mdd: avoid logging trusted.som xattr in changelogs

The Lazy Size on MDT is causing the trusted.som xattr to be logged
in the changelog whenever a file is needed to update this xattr
data casued by file open/close or truncate operations.
This patch fixes this problem to avoid logging this xattr for
every file.

Signed-off-by: Qian Yingjin <qian@ddn.com>
Change-Id: I8f069afdfa84a8fc9f96819d066fd3e4d08794af
Reviewed-on: https://review.whamcloud.com/33323
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Wang Shilong <wshilong@ddn.com>
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>