- Eliminate the use of a recursive mutex.
- Mark the driver INTR_MPSAFE.
This work is incomplete and will be refined in a future commit.
- Most notably, _locked() variants of entry points need to be introduced.
- The mii upcall/downcall may still be racy.
- Add a stubbed-out guard against racing rl_detach() for the time being.
Tested on: UP, debug.mpsafenet && !debug.mpsafenet
Reviewed by: silence on -net