netkit: Remove explicit active/peer ptr initialization

Remove the explicit NULLing of active/peer pointers and rely on the
implicit one done at net device allocation.

Suggested-by: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: Nikolay Aleksandrov <razor@blackwall.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20231026094106.1505892-2-razor@blackwall.org