interface: fs: add fs.getdents function

interface/fs.xpc

@@ -3,9 +3,11 @@ interface fs 6400;
 func open[0](path: string, flags: int) -> (err: int);
 func close[1]() -> (err: int);
 
-func read[2](count: size) -> (err: int, nr_read: size, data: buffer);
+func read[2](count: size) -> (err: int, data: buffer);
 func write[3](data: buffer) -> (err: int, nr_written: size);
 
 func seek[4](offset: offset, origin: int) -> (err: int, new_pos: offset);
 
 func map[5](prot: int, flags: int) -> (err: int, vmo: handle);
+
+func getdents[6]() -> (err: int, dents: buffer);