Each mechanism driver loaded in the ML2Plugin can provide what
extensions are supported. By default, any mech driver can support
all extensions.
This extension filtering is done during the plugin initialization.
If any requested extension is not supported, it will be silently
removed from the loaded extensions.
Depends-On: https://review.opendev.org/#/c/743519
Related-Bug: #1888829
Change-Id: Id4809d4f3c4e13a93f9160df3618f8602b57437c