wifi: Add SoftAp Max Client control support

1. SoftAp Max Client parameter in SoftApConfiguration
2. Add new field in CarrierConfigManager to get carrier max client
setting.
3. Add new Callback: onCapabilityChanged to notify Settings to know
current supported maximum client number from carrier req and chip limit.

Bug: 142752869
Test: atest frameworks/base/wifi/tests/
Change-Id: I03366e22055233b9f77e0c1808e54a473569c9c7