handle padding properly

src/lib.rs

@@ -494,6 +494,8 @@ where
         return Ok((input, None));
     }
 
+    let (input, _padding) = take(attr_len % 4)(input)?;
+
     let attr = match attr_type {
         ATTR_MAPPED_ADDRESS => {
             let (_residual, addr) = parse_stun_address(attr_data)?;