Bump the timeout in p2p_ibd_stalling

Summary: This test fails regularly to receive the block data before the timeout triggers on our slow osx CI machine.

Test Plan:

./test/functional/test_runner.py p2p_ibd_stalling

Reviewers: #bitcoin_abc, roqqit

Reviewed By: #bitcoin_abc, roqqit

Differential Revision: https://reviews.bitcoinabc.org/D17586