bpf: expose prog id for cls_bpf and act_bpf

In order to be able to retrieve the attached programs from cls_bpf
and act_bpf, we need to expose the prog ids via netlink so that
an application can later on get an fd based on the id through the
BPF_PROG_GET_FD_BY_ID command, and dump related prog info via
BPF_OBJ_GET_INFO_BY_FD command for bpf(2).

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/pkt_cls.h

@@ -369,6 +369,7 @@ enum {
 	TCA_BPF_FLAGS,
 	TCA_BPF_FLAGS_GEN,
 	TCA_BPF_TAG,
+	TCA_BPF_ID,
 	__TCA_BPF_MAX,
 };