OPENAFS-SA-2016-002 AFSStoreStatus information leak

OPENAFS-SA-2016-002 AFSStoreStatus information leak

Marc Dionne reported that portions of the AFSStoreStatus structure
were not written to before being sent over the network for
operations such as create, symlink, etc., leaking the contents
of the kernel stack to observers.  Which fields in the request
are used are controlled by a flags field, and so if a field was
not going to be used by the server, it was sometimes left
uninitialized.

Fix the information leak by zeroing out the structure before use.

FIXES 132847

Change-Id: I84a5a10442732ebbcb5d5067ca22030fb795168b