lib/netlink-protocol.h: Do not include headers for windows kernel build.

Added saurabh's fix to not to include some header files
in lib/netlink-protocol.h not needed by windows driver.

This is a temporary fix to make sure that windows driver can compile.

We are working in parallel on adding netlink support in windows driver
(https://github.com/openvswitch/ovs-issues/issues/18). With netlink support
changes we will get rid of the dependency on lib/netlink-protocol.h.

Testing:
1. Verified make distcheck on linux.
2. Verified that windows driver can compile now.
3. Verified that ping works over vxlan tunnel.

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-at: https://github.com/openvswitch/ovs-issues/issues/21
Signed-off-by: Ben Pfaff <blp@nicira.com>