The patch provides the same socket option as Linux IP_ORIGDSTADDR.
Unfortunately they will have different integer value due to Linux value being already assigned in FreeBSD.

The patch is similar to IP_RECVDSTADDR but also provides the destination port value to the application.

This allows/improves implementation of transparent proxies on UDP sockets due to having the whole information on forwarded packets.

Sponsored-by: rsync.net
Differential Revision: D9235
Reviewed-by: adrian