bpf: add helper for retrieving current numa node id

Use case is mainly for soreuseport to select sockets for the local
numa node, but since generic, lets also add this for other networking
and tracing program types.

Suggested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/bpf.h

@@ -426,6 +426,12 @@ enum bpf_func_id {
 	 */
 	BPF_FUNC_set_hash_invalid,
 
+	/**
+	 * bpf_get_numa_node_id()
+	 * Returns the id of the current NUMA node.
+	 */
+	BPF_FUNC_get_numa_node_id,
+
 	__BPF_FUNC_MAX_ID,
 };