Add iOS support for getWifiIP ported from cordova-plugin-networkinterface lib

[digaus]

iOS doesn't currently support getWifiIP, can be ported from cordova-plugin-networkinterface?

[tripflex]

So you used the issue template but didn't put any information in this issue.

Specifically you're referring to: https://github.com/salbahra/cordova-plugin-networkinterface/blob/master/src/ios/CDVNetworkInterface.m#L128

Which uses: https://github.com/salbahra/cordova-plugin-networkinterface/blob/master/src/ios/CDVNetworkInterface.m#L5

I don't have any iOS devices to test this with, but it shouldn't be too hard to port this over, will just need some people with iOS devices to test this for us

[digaus]

@tripflex

Got a mac and an iPad, will provide a PR soon, so be prepared ;)