feat: macOS and FreeBSD reuse the same code

[meowtec]

What's changed:

1. Add [[example]] section into Cargo.toml so that we can easily run example: cargo run --example example.
2. The current implement for local_ip on bsd is wrong as it return 127.0.0.1. (tested on freebsd 13 virtual machine).
3. macOS and bsd should use same code because there are very few differences between each other.
4. Support for Android via libc::getifaddrs because neli can not compile targeting Android.