[network_info_plus] Missing method wifiIPv6Address on MacOS implementation

[miquelbeltran]

Calling to getWifiIPv6 will cause an error on MacOS.

The platform channel method is missing here:

plus_plugins/packages/network_info_plus/network_info_plus_macos/macos/Classes/NetworkInfoPlusPlugin.swift

Line 36 in fc4ea21

public func handle(_ call: FlutterMethodCall, result: @escaping FlutterResult) {