staging: lustre: ldlm: xattr locks are lost on mdt

On the server side mdt_intent_getxattr() can return EFAULT if a
buffer cannot be found, it is returned after lock_replace, where a
new lock is installed into lockp. An error forces ldlm_lock_enqueue()
to destroy the original lock, but ldlm_handle_enqueue0() drops the
reference on the new lock. The xattr client code implied intent
error is returned under a lock, which is immediately cancelled.
Check if a lock obtained and cancel it properly for error cases.
Note: we should support both cases for interop needs, an intent
error under a lock and with a lock abort. Keep returning a lock
with an intent error for interop purposes for now, to be dropped
later when client will get old enough. make all intent ops to
work through md_intent_lock: getxattr and layout, which should
extract the intent error.

Signed-off-by: Vitaly Fertman <vitaly.fertman@seagate.com>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-7433
Seagate-bug-id: MRP-3072 MRP-3137
Reviewed-on: http://review.whamcloud.com/17220


Reviewed-by: Andrew Perepechko <andrew.perepechko@seagate.com>
Reviewed-by: Andriy Skulysh <andriy.skulysh@seagate.com>
Tested-by: Elena V. Gryaznova <elena.gryaznova@seagate.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Lai Siyao <lai.siyao@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>