Recent commit uses a Socket constructor not available on mono (causes a crash)

[borgdylan]

Looking at the line https://github.com/aspnet/KRuntime/blob/dev/src/Microsoft.Framework.Runtime/DefaultHost.cs#L171, a constructor not available on mono is being used triggering teh following exception:

Missing method System.Net.Sockets.Socket::.ctor(SocketType,ProtocolType) in assembly /usr/lib/mono/gac/System/4.0.0.0__b77a5c561934e089/System.dll, referenced in assembly /home/dylan/.kre/packages/KRE-mono45-x86.1.0.0-alpha4-10274/bin/Microsoft.Framework.Runtime.dll
Method not found: 'System.Net.Sockets.Socket..ctor'.

The only overloads available on mono are:
public Socket (AddressFamily addressFamily, SocketType socketType, ProtocolType protocolType)
public Socket (SocketInformation socketInformation)

[alek-sys]

I've tried to fix it in #529 (but probably in pretty straightforward way)