default route's interface discovery code has stopped working

[karlkleinpaste]

i don't know when it happened, much less how, but the code that discovers the default route and its interface address no longer works. i've had this code in place since 2014, so i'm mystified as to what underlying interface changed.

solution will be to eliminate the entire rtnetlink-driven nightmare. just read /proc/net/route directly, and find destination "00000000". use that interface, compare that interface against the set of interfaces returned by getifaddrs(3) (as before).