bpf: flowlabel in bpf_fib_lookup should be flowinfo

As Michal noted the flow struct takes both the flow label and priority.
Update the bpf_fib_lookup API to note that it is flowinfo and not just
the flow label.

Cc: Michal Kubecek <mkubecek@suse.cz>
Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

include/uapi/linux/bpf.h

@@ -2629,7 +2629,7 @@ struct bpf_fib_lookup {
 	union {
 		/* inputs to lookup */
 		__u8	tos;		/* AF_INET  */
-		__be32	flowlabel;	/* AF_INET6 */
+		__be32	flowinfo;	/* AF_INET6, flow_label + priority */
 
 		/* output: metric of fib result (IPv4/IPv6 only) */
 		__u32	rt_metric;