ipv6: sr: add code base for control plane support of SR-IPv6

This patch adds the necessary hooks and structures to provide support
for SR-IPv6 control plane, essentially the Generic Netlink commands
that will be used for userspace control over the Segment Routing
kernel structures.

The genetlink commands provide control over two different structures:
tunnel source and HMAC data. The tunnel source is the source address
that will be used by default when encapsulating packets into an
outer IPv6 header + SRH. If the tunnel source is set to :: then an
address of the outgoing interface will be selected as the source.

The HMAC commands currently just return ENOTSUPP and will be implemented
in a future patch.

Signed-off-by: David Lebrun <david.lebrun@uclouvain.be>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/seg6_genl.h

@@ -0,0 +1,32 @@
+#ifndef _UAPI_LINUX_SEG6_GENL_H
+#define _UAPI_LINUX_SEG6_GENL_H
+
+#define SEG6_GENL_NAME		"SEG6"
+#define SEG6_GENL_VERSION	0x1
+
+enum {
+	SEG6_ATTR_UNSPEC,
+	SEG6_ATTR_DST,
+	SEG6_ATTR_DSTLEN,
+	SEG6_ATTR_HMACKEYID,
+	SEG6_ATTR_SECRET,
+	SEG6_ATTR_SECRETLEN,
+	SEG6_ATTR_ALGID,
+	SEG6_ATTR_HMACINFO,
+	__SEG6_ATTR_MAX,
+};
+
+#define SEG6_ATTR_MAX (__SEG6_ATTR_MAX - 1)
+
+enum {
+	SEG6_CMD_UNSPEC,
+	SEG6_CMD_SETHMAC,
+	SEG6_CMD_DUMPHMAC,
+	SEG6_CMD_SET_TUNSRC,
+	SEG6_CMD_GET_TUNSRC,
+	__SEG6_CMD_MAX,
+};
+
+#define SEG6_CMD_MAX (__SEG6_CMD_MAX - 1)
+
+#endif