LU-10912 mdc: use large xattr buffers for old servers

LU-10912 mdc: use large xattr buffers for old servers

Pre 2.10.1 MDTs will crash when they receive a listxattr (MDS_GETXATTR
with OBD_MD_FLXATTRLS) RPC for an orphan or dead object. So for
clients connected to these older MDTs, try to avoid sending listxattr
RPCs by making the bulk getxattr (MDS_GETXATTR with OBD_MD_FLXATTRALL)
more likely to succeed and thereby reducing the chances of falling
back to listxattr.

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: Ia96323c47c91a44495b73be2d95705298c7f7ac9
Reviewed-on: https://review.whamcloud.com/31990
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Jenkins
Reviewed-by: Fan Yong <fan.yong@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>