Motivation

Being able to run ethereum_rust with kurtosis localness without disabling network-related code.
This PR fixes a couple panic sources when running with kurtosis:

• panics with out of bounds when accessing kademlia tables
• panics when sending messages to socket addresses built from ivp6 node ips

Unsolved issues that still cause panics:

• Some neighbour messages incoming from kurtosis have udp port set to 0

Description

• Uses saturating sub when calculating kademlia bucket numbers
• Converts ivp6 node ips into ipv4 when building socket addresses from neighbors

Closes None