UDPv4 features to UDPv6:
- Add MAC checks on delivery and MAC labeling on transmit.
- Check for (and reject) datagrams with destination port 0.
- For multicast delivery, check the source port only if the socket being
considered as a destination has been connected.
- Implement UDP blackholing based on net.inet.udp.blackhole.
- Add a new ICMPv6 unreachable reply rate limiting category for failed
delivery attempts and implement rate limiting for UDPv6 (submitted by
bz).
Approved by: re (kensmith)
Reviewed by: bz
08af97b790