LU-4222 mdt: extra checking for getattr RPC.

LU-4222 mdt: extra checking for getattr RPC.

Check whether getattr RPC can hold layout MD(RMF_MDT_MD),
in case the client sends some invalid RPC, which can
cause panic on MDT.

Client will retrieve cl_max_md_size/cl_default_md_size
from MDS during mount process, so it will initialize
cl_max_md_size/cl_default_md_size before sending getattr
to MDS.

Signed-off-by: wang di <di.wang@intel.com>
Change-Id: I43bbe54c37360242bb7a3cd2aa8d90c2b9e0baf1
Reviewed-on: http://review.whamcloud.com/8599
Reviewed-by: Fan Yong <fan.yong@intel.com>
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>