dragonball: Remove with-serde feature assertion

Code inside `test_mac_addr_serialization_and_deserialization` test does
not actually require this `with-serde` feature to test, removing the
assertion here to enable this test.

Signed-off-by: Ruoqing He <heruoqing@iscas.ac.cn>

src/dragonball/dbs_utils/src/net/mac.rs

@@ -146,7 +146,6 @@ mod tests {
         assert!(MacAddr::from_bytes(&src3[..]).is_err());
     }
 
-    #[cfg(feature = "with-serde")]
     #[test]
     fn test_mac_addr_serialization_and_deserialization() {
         let mac: MacAddr =