tc: cls_bpf: rename bpf_len to bpf_num_ops

It was suggested by DaveM to change the name as "len" might indicate
unit bytes.

Suggested-by: David Miller <davem@davemloft.net>
Signed-off-by: Jiri Pirko <jiri@resnulli.us>
Acked-by: Daniel Borkmann <dborkman@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>