bpf, docs: Fix bpf_redirect_peer header doc

Amend the bpf_redirect_peer() header documentation to also mention
support for the netkit device type.

Signed-off-by: Victor Stewart <v@nametag.social>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20240116202952.241009-1-v@nametag.social


Signed-off-by: Alexei Starovoitov <ast@kernel.org>