datapath-windows: Make GET_PID a separate IOCTL

datapath-windows: Make GET_PID a separate IOCTL

Added a new IOCTL in order to retrieve the PID from the kernel datapath.
The new method uses a direct and cleaner way, as opposed to the old way
of using a Netlink transaction, avoiding the unnecessary overhead.

Signed-off-by: Sorin Vinturis <svinturis@cloudbasesolutions.com>
Reported-by: Alin Gabriel Serdean <aserdean@cloudbasesolutions.com>
Reported-at: https://github.com/openvswitch/ovs-issues/issues/31
Acked-by: Nithin Raju <nithin@vmware.com>
Acked-by: Alin Gabriel Serdean <aserdean@cloudbasesolutions.com>
Tested-by: Alin Gabriel Serdean <aserdean@cloudbasesolutions.com>
Signed-off-by: Ben Pfaff <blp@nicira.com>