gd/hci: MSFT operations disallowed if not supported

The MSFT monitor add/remove/enable operations should not be executed
on non-supporting platforms.

Bug: 270629001
Tag: #floss
Test: ./build.py --target test
Test: Manual test on a ChromeOS device that does not support the MSFT
extension, e.g., octopus/blooglet
  localhost # btclient
  bluetooth> le-scan register-scanner
  bluetooth> le-scan start-scan 1
  bluetooth> le-scan stop-scan 1
The btadapterd should not crash. The btclient outputs messages like
  msft_adv_monitor_enable: Disallowed as MSFT extension is not supported

Change-Id: I416010b0196706e93bf0607b50382eebf0c1f91b