MTU: Support ios, tvos and visionos

[mxinden]

iOS does not ship with <net/route.h>, see https://github.com/mozilla/mtu/issues/82.

mozilla/mtu#83 dropped support for the Apple OS variants, see e.g. code below:

https://github.com/mozilla/mtu/blob/8329753853c5cc0b695a8b72f953f8a1b9828c24/build.rs#L47-L52

https://github.com/mozilla/mtu/blob/8329753853c5cc0b695a8b72f953f8a1b9828c24/src/lib.rs#L101-L107

We should add support for target_os ios, tvos and visionos in the future.