net: comment fixes against BPF devmap helper calls

Update BPF comments to accurately reflect XDP usage.

Fixes: 97f91a7c

 ("bpf: add bpf_redirect_map helper routine")
Reported-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>