[avalanche] decrease the number of GETAVAADDR spamming iterations and bump the timeout

Summary:
This test sometimes fails n CI because the expected log message is seen after the default assert_debug_log 2 seconds timeout. Bump the timeout to make the failure less likely to happen.
Also reduce the number of iterations to 2 to speedup the test. The choice of 10 iterations was arbitrary, and does not prove anything.

Test Plan: ninja check-functional

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D12524