Fix the abc_p2p_avalanche functional tests for ARM

Summary:
The test is failing on slow machines, especially when using qemu (ARM
and AArch64).

Test Plan:

ninja check-functional
./contrib/teamcity/build-configurations.py buld-linux-arm
./contrib/teamcity/build-configurations.py buld-linux-aarch64

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D9347