net: Add interrupt to pcp retry loop

Summary:
Without this interrupt bitcoind takes a long time to exit if requested
to do so after a failed pcp lookup on startup.

This is a backport of core#33338
Depends on D19803

Test Plan: ninja all check-all

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D19804