Floss: Allow set log level from btclient

In some cases we want to ask user to provide verbose logs but this is
impossible if they are not in developer mode.

This implements the commands in btclient to set and get the current log
level via btclient.

Bug: 369506387
Tag: #floss
Test: mmm packages/modules/Bluetooth
Test: Deploy to ciri and verified manually
Flag: EXEMPT, Floss-only changes
Change-Id: I38777d0d66c9f570b944c018389215919e8f0064