Support additional `recvmsg` ancillary messages

[max-heller]

Similar to nix::sys::socket::ControlMessageOwned, it'd be great for rustix::net::RecvAncillaryMessage to be able to handle ancillary messages beyond SCM_RIGHTS and SCM_CREDS, in particular the timestamp variants e.g. SCM_TIMESTAMP

[eminence]

I'd be interested in seeing support for IP_TOS which gives access to the Type-Of-Service byte (which includes the two-bit ECN field)