LU-5453 mdt: mdt_reint_setattr() and mdt_attr_set() fixes

LU-5453 mdt: mdt_reint_setattr() and mdt_attr_set() fixes

In mdt_reint_setattr() add early checks that the object exists and is
local. Remove the invalid assertion in mdt_attr_set() that the object
is local. Replace several assertions on wire data with -EPROTO
returns. In mdt_attr_set() when locking the slaves of a striped
directory use a PW lock for slave 0. Remove the unused flags parameter
of mdt_attr_set().

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: I2aa5a645b8398c1e2890291cb61ffa280ec82443
Reviewed-on: http://review.whamcloud.com/11353
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: wangdi <di.wang@intel.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>