datapath-windows: make NL version a UIN8 and add a validateDp arg

datapath-windows: make NL version a UIN8 and add a validateDp arg

I didn't realize earlier that version in a netlink message was a
UINT8. So, fixing that here.

Also, some of the commands don't pass a valid DP value. Hence adding
a field to identify such commands.

Signed-off-by: Nithin Raju <nithin@vmware.com>
Signed-off-by: Ankur Sharma <ankursharma@vmware.com>
Acked-by: Ankur Sharma <ankursharma@vmware.com>
Acked-by: Saurabh Shah <ssaurabh@vmware.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>