Potential issues with statistics for interfaces with a lot of routes

[j-chmielewski]

Original issue: DefGuard/client#617.
Partially addressed in #100.

There may still be issues remaining as mentioned in #100 (comment), because AllowedIps are not currently merged. This shouldn't impact Defguard, as the affected logic is only used for statistics, not for interface setup.

TODO:

• Reproduce and confirm whether the issue occurs.
• Also check if other fields in the Peer struct require more nuanced merge logic.