Fix for UDP broadcast

Right now, if you'll try to use Network target and specify address="udp://255.255.255.255:9090" (255.255.255.255 is udp broadcast address, i.e. all messages sent to this address will be broadcasted to all machines inside this local network) in nlog config file, NLog will not send messages over udp. You need to excplicitly set EnableBroadcast in System.Net.Sockets.Socket to true. This pull request fixes this problem.

http://msdn.microsoft.com/en-us/library/windows/desktop/ms740668(v=vs.85).aspx#WSAEACCES here you can find some information about this.