fix applying IP filter to DHT traffic (HanabishiRecca)

[arvidn]

adresses #7789

[HanabishiRecca]

I want to mention again that this patch does not block the interaction with banned IPs completely. It's more a partial workaroud.

dht_tracker itself simply lacks any filtering logic. I.e. incoming_packet() still accepts all incoming traffic, send_packet() still communicates with a banned peer when it manages to make it into the DHT node list somehow.

[arvidn]

right, makes sense