p2p: Use mocktime for ping timeout

Summary:

It is slightly confusing to use mocktime for some times, but not others.

Start fixing that by making the ping timeout use mocktime.

This is a backport of core#23218
Depends on D10956

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D10957