datapath-windows: Implement event read handler.

The Read event handler is executed when user mode issues a socket
receive on an MC socket associated with the event queue. A new IOCTL
READ command is used to differentiate between transaction based and packet
miss sockets.
An entry for the handler will be added once the Control family (logically
should have been added to the Vport family)
implementation checked in.
User mode code for setting the socket type will follow

Signed-off-by: Eitan Eliahu <eliahue@vmware.com>
Acked-by: Ankur Sharma <ankursharma@vmware.com>
Acked-by: Nithin Raju <nithin@vmware.com>
Acked-by: Alin Gabriel Serdean <aserdean@cloudbasesolutions.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>