[net] Add extra entropy to the version message

Summary:
This ensures we have 128 bits of entropy to play with, which can be used as a cryptographic challenge. 64bits is not enough for this.

Depends on D8860

Test Plan:

ninja all check-all

Reviewers: #bitcoin_abc, majcosta

Reviewed By: #bitcoin_abc, majcosta

Subscribers: majcosta

Differential Revision: https://reviews.bitcoinabc.org/D8861