netlink: move docs to README

kernel_module/netlink.h

@@ -0,0 +1,10 @@
+#ifndef NETLINK_H
+#define NETLINK_H
+
+/* Socket identifier, matches userland. TODO can be anything?
+ * Is there a more scalable way to do it? E.g. ioctl device,
+ * kernel generates one on the fly, then give it back and connect?
+ * https://stackoverflow.com/questions/32898173/can-i-have-more-than-32-netlink-sockets-in-kernelspace */
+#define NETLINK_USER 31
+
+#endif