Missing RTF_*, RTA_*, RTAX_*, RTM_* definitions on BSDs #3711
Description
Target: x86_64-unknown-dragonfly, x86_64-unknown-freebsd, x86_64-unknown-netbsd, x86_64-unknown-openbsd
API: BSD 4.3 Reno (historic), DragonFly, FreeBSD, NetBSD, OpenBSD
Test case: n0-computer/iroh#2306
See also: downstream fix, copy-pasted from macOS and likely incorrect/incomplete