odp-netlink.h: Autogenerate a version of odp-netlink for windows kernel.

Autogenerated odp-netlink.h will not compile with windows kernel, as
it refers to some userspace files like openvswitch/types.h and
packets.h which hyperv extension does not access. Due to this the
windows datapath compilation is broken on tip of tree. This patch
intends to fix that.

In this patch we add a new sed script "extract-odp-netlink-windows-dp-h"
to create OvsDpInterface.h. It works on similar lines as
extract-odp-netlink-h, but avoids including the header files
which are not available for driver.

After this fix, a userspace build will be needed before windows
kernel datapath can be built.

Tested that hyperv extension could be built after building
the userspace. Verified vxlan tunnel based ping across
hypervisors. Verified that odp-netlink-windows-dp.h is not
built for linux platform. Ran 'make distcheck' to verify that
nothing is broken on linux.

Signed-off-by: Ankur Sharma <ankursharma@vmware.com>
Co-authored-by: Saurabh Shah <ssaurabh@vmware.com>
Tested-by: Ankur Sharma <ankursharma@vmware.com>
Reported-by: Alin Serdean <aserdean@cloudbasesolutions.com>
Reported-by: Nithin Raju <nithin@vmware.com>
Reported-at: https://github.com/openvswitch/ovs-issues/issues/21
Signed-off-by: Ben Pfaff <blp@nicira.com>