NFSv4: Ensure we do not reuse open owner names

The NFSv4 spec is ambiguous about whether or not it is permissible
to reuse open owner names, so play it safe. This patch adds a timestamp
to the state_owner structure, and combines that with the IDA based
uniquifier.
Fixes a regression whereby the Linux server returns NFS4ERR_BAD_SEQID.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
diff --git a/fs/nfs/nfs4_fs.h b/fs/nfs/nfs4_fs.h
index 97ecc86..b6db9e3 100644
--- a/fs/nfs/nfs4_fs.h
+++ b/fs/nfs/nfs4_fs.h
@@ -59,6 +59,7 @@
 
 #define NFS_SEQID_CONFIRMED 1
 struct nfs_seqid_counter {
+	ktime_t create_time;
 	int owner_id;
 	int flags;
 	u32 counter;