NFSD: prevent underflow in nfssvc_decode_writeargs()

Smatch complains:

	fs/nfsd/nfsxdr.c:341 nfssvc_decode_writeargs()
	warn: no lower bound on 'args->len'

Change the type to unsigned to prevent this issue.

Cc: stable@vger.kernel.org
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

fs/nfsd/nfsproc.c

@@ -230,7 +230,7 @@ nfsd_proc_write(struct svc_rqst *rqstp)
 	unsigned long cnt = argp->len;
 	unsigned int nvecs;
 
-	dprintk("nfsd: WRITE    %s %d bytes at %d\n",
+	dprintk("nfsd: WRITE    %s %u bytes at %d\n",
 		SVCFH_fmt(&argp->fh),
 		argp->len, argp->offset);
 

fs/nfsd/xdr.h

@@ -32,7 +32,7 @@ struct nfsd_readargs {
 struct nfsd_writeargs {
 	svc_fh			fh;
 	__u32			offset;
-	int			len;
+	__u32			len;
 	struct xdr_buf		payload;
 };