- ADDED: Support to read out Interface flags on OS X

Prior to these changes the NetworkInterface class provided very little information about the capabilities of the available network interfaces, especially not about their multicast capabilities and / or their OperationalStatus.

- ADDED: Implemented NetworkInterface property "OperationalStatus" to be UP, in case the IFF_UP flag is set
- ADDED: Implemented NetworkInterface property "SupportsMulticast" to be true, in case the IFF_MULTICAST flag is set

This change is released under the MIT license.