flexfiles: enforce per-mirror stateid only for v4 DSes

Since commit bb21ce0a we always enforce per-mirror stateid.
However, this makes sense only for v4+ servers.
Signed-off-by: NTigran Mkrtchyan <tigran.mkrtchyan@desy.de>
Signed-off-by: NTrond Myklebust <trond.myklebust@hammerspace.com>

fs/nfs/flexfilelayout/flexfilelayout.c

@@ -1733,7 +1733,8 @@ ff_layout_read_pagelist(struct nfs_pgio_header *hdr)
 	if (fh)
 		hdr->args.fh = fh;
 
-	if (!nfs4_ff_layout_select_ds_stateid(lseg, idx, &hdr->args.stateid))
+	if (vers == 4 &&
+		!nfs4_ff_layout_select_ds_stateid(lseg, idx, &hdr->args.stateid))
 		goto out_failed;
 
 	/*
@@ -1798,7 +1799,8 @@ ff_layout_write_pagelist(struct nfs_pgio_header *hdr, int sync)
 	if (fh)
 		hdr->args.fh = fh;
 
-	if (!nfs4_ff_layout_select_ds_stateid(lseg, idx, &hdr->args.stateid))
+	if (vers == 4 &&
+		!nfs4_ff_layout_select_ds_stateid(lseg, idx, &hdr->args.stateid))
 		goto out_failed;
 
 	/*