wifi: Add metrics for bridged AP use case

1. Add a new metrics DUAL_AP_UP to store dual AP information.
2. Add a new metrics num_connected_clients_on_current_frequency to store
client number on current instance. And add frequency info into NUM_CLIENTS_CHANGED

Bug: 168306843
Test: atest -c FrameworksWifiTests
Updated-PDD: TRUE
Change-Id: Ia9cb2233bf52dc5c31950749b4e392bf9df2edc6
5 files changed