I couldn't work out where this went missing from "git log", but it became
important with the switch to hidden visibility.
Change-Id: I921f81e36642a2c65c3ec85dc9b5b87c5d977a5b
Replace iface cache key with netid.
Replace _mark with netid.
Mark sockets used to test IPv4/IPv6 support as well as sockets
used to determine source address for rfc6724 sort.
Remove pid/uid mappings (functionality moved to system/netd).
Do not create resolv_cache when it does not exist, but rather only
when DNS configuration is supplied.
Clean up unused functions.
Change-Id: I9ccfda2902cc0943e87c9bc346ad9a2578accdab
