hostap: SAP mode needs more heap

SAP mode adds more functionality that increases the heap usage, based on
experiments, 40000 works well to avoid startup failures.

Signed-off-by: Chaitanya Tata <Chaitanya.Tata@nordicsemi.no>
Signed-off-by: Jukka Rissanen <jukka.rissanen@nordicsemi.no>