feature: provide InterfaceMultiaddrsFor

[tobil4sk]

net.InterfaceAddrs calls fail on android. This function allows specifying your own set of addresses, so another api can be used to avoid the issue.

See: #255 (comment)

Closes #255

[MarcoPolo]

Is the idea that you'll override these functions with go:linkname?

[tobil4sk]

The way I'm using it is to always use InterfaceMultiaddrsFor instead of InterfaceMultiaddrs, which allows any api to be used to get the addresses.

I'm quite new to go so I'm not familiar with go:linkname. This is how I've patch a library that relies on go-multiaddr in line with this change: libp2p/go-libp2p#3236

[MarcoPolo]

Can you show me how you'll use this change? I'm having a hard time understanding how exposing InterfaceMultiaddrsFor helps here. Thanks

[tobil4sk]

Can you show me how you'll use this change? I'm having a hard time understanding how exposing InterfaceMultiaddrsFor helps here. Thanks

Instead of relying on InterfaceMultiaddrs, a slice of net.Addr can be passed into InterfaceMultiaddrsFor which allows the caller to decide how to determine the addresses. See the line:
https://github.com/libp2p/go-libp2p/pull/3236/files#diff-46c1cc328c2b33cbdce1bc123a2d6e06f5afc4758186638f9320673f8595ab0bR523

Additionally, when using manet.ResolveUnspecifiedAddresses, you have to avoid passing nil as the second argument to prevent it from calling InterfaceMultiaddrs internally. E.g.:
https://github.com/libp2p/go-libp2p/pull/3236/files#diff-e544d19687434c7b654de15689302596c5159444ad1db181f7096473eb42e8f3R56-R68