Lossy serialization of SocketAddrV6

[benmaddison]

The non-human readable serialization of SocketAddrV6 (and by extension SocketAddr) encodes only IP address and port information, omitting flow info and scope:

serde/serde/src/ser/impls.rs

Lines 857 to 874 in ddc1ee5

	#[cfg(feature = "std")]
	impl Serialize for net::SocketAddrV6 {
	fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
	where
	S: Serializer,
	{
	if serializer.is_human_readable() {
	const MAX_LEN: usize = 58;
	debug_assert_eq!(
	MAX_LEN,
	"[1001:1002:1003:1004:1005:1006:1007:1008%4294967295]:65000".len()
	);
	serialize_display_bounded_length!(self, MAX_LEN, serializer)
	} else {
	(self.ip(), self.port()).serialize(serializer)
	}
	}
	}

I have already dug around the commit logs to see if there was a reason, but as far as I can tell it was just an oversight.

The fix is obvious and trivial, and I'm happy to do the PR. But before doing so I wanted to find out whether there is some existing mechanism to use when introducing backwards incompatible changes to serialized representations like this?