net: Drop only invalid entries when reading banlist.json

Summary:
Currently all entries in the file are dropped. Fix that by only dropping the invalid ones

This is a backport of core#22362 and core#26229
Depends on D19134

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D19135