Add Network up check

[remco1271]

Fix crash when network is down.
Checks first if network is up before sending data
Because you can't open a socket on a network interface that is down.

[whysguy52]

can a similar change be made to the EEIPClient.cs in the EEIP.dll?

something like this?

if (networkInterface.OperationalStatus != OperationalStatus.Up || networkInterface.NetworkInterfaceType != NetworkInterfaceType.Wireless80211 && networkInterface.NetworkInterfaceType != NetworkInterfaceType.Ethernet)
{
    continue;
}

I currently have the method copied and pasted into my own class and just doing the extra check but would be cool if it was in the source file.

:) love this library btw.