qcacld-3.0: Increase the scan database size to 500 from 300

In very noisy environment and with 6 GHz co-located AP, scan
database size of 300 might not be enough.

So increase the size to 500.

Change-Id: I26077b2ab0d24f73a7c8e29990504d5b284eccf4
CRs-Fixed: 3395834