datapath-windows: Upcall NL packet format: Queue elem for packe in NL format.

datapath-windows: Upcall NL packet format: Queue elem for packe in NL format.

[1] Allocate a queue element and space to hold the packet, key, tunnel key
and user data in NL format.
[2] Format the NL header
[3] Store packet, key, tunnel key and user data in NL format
[4] Calculates and insert checksum if offloaded.

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