macOS doing a shared library build is not working without untangling
some of the interdependencies. This commit does that, at least enough
to get macOS to compile.
This isn't the cleanest as currently implemented (we have some net/
things in `liblokinet-platform` and some in `liblokinet`, and likewise
ev/vpnio.cpp is in `liblokinet` while the rest of `ev/*` is in
`liblokinet-platform`).
- Move IPRange into its own net/ip_range.hpp
- Move the static net::IPPacket::TruncateV6, etc. functions to free
net::TruncateV6, etc. functions (now from net/ip.hpp instead of
net/ip_packet.hpp).
- Make net::TruncateV6 and net::ExpandV4 constexpr.
- Add IPRange::FromIPv4 factory function (to replace the iprange_ipv4
free function)
Rename net/ip.{cpp,hpp} to net/ip_packet.{cpp,hpp}.
(Doing this in two commits because I want to repurpose ip.hpp/ip.cpp,
and want git to figure out the history properly).
