NFS: Account for NFS bytes read via the splice API

Bytes read via the splice API should be accounted for in the NFS
performance statistics.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

fs/nfs/file.c

@@ -284,8 +284,11 @@ nfs_file_splice_read(struct file *filp, loff_t *ppos,
 		(unsigned long) count, (unsigned long long) *ppos);
 
 	res = nfs_revalidate_mapping(inode, filp->f_mapping);
-	if (!res)
+	if (!res) {
 		res = generic_file_splice_read(filp, ppos, pipe, count, flags);
+		if (res > 0)
+			nfs_add_stats(inode, NFSIOS_NORMALREADBYTES, res);
+	}
 	return res;
 }