NFSv4: Fix return values for nfs4_file_open()

Currently, we are translating RPC level errors such as timeouts,
as well as interrupts etc into EOPENSTALE, which forces a single
replay of the open attempt. What we actually want to do is
force the replay only in the cases where the returned error
indicates that the file may have changed on the server.

So the fix is to spell out the exact set of errors where we want
to return EOPENSTALE.

Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>