tests: Bluetooth: Mesh: adapt bsim beacon tests for ext adv

Beacon test had trick for extended advertiser. That has been added as
conditional compilation. Additionally, waiting beacon procedure
waits for 1 more second to avoid boundary case since
the extended advertiser is more precisionive.

Signed-off-by: Aleksandr Khromykh <aleksandr.khromykh@nordicsemi.no>