NFSv4.1: Allow getdeviceinfo to return notification info back to caller

We are only allowed to cache deviceinfo if the server supports notifications
and actually promises to call us back when changes occur. Right now, we
request those notifications, but then we don't check the server's reply.

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

diff --cc fs/nfs/nfs4proc.c
Simple merge

diff --cc fs/nfs/nfs4xdr.c
Simple merge

diff --cc include/linux/nfs_xdr.h
Simple merge