staging: lustre: 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>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-4222
Reviewed-on: http://review.whamcloud.com/8599


Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>