datapath-windows: add a context structure for user parameters

datapath-windows: add a context structure for user parameters

In this patch we add a context structure for collecting all the parameters
passed from usersapce in one place. The idea is to reduce the number of
parameters being passed to the netlink command handler functions.

It can be argued that not all functions require all the arguments, but this
approach keeps the code clean, IMO.

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>