DragonFlyBSD

On master using UP kernel our default usched (dfly) crash on boot.

Using bsd4 usched works (kern.user_scheduler="bsd4").

UP kernel doesn't build, as WERROR triggers on some unused var, this is trivially fixed.

Should we fix dfly usched or just declare it SMP only (and bsd4 as default on UP)?

I guess UP system will have no benefit from dfly, vs bsd4.

(another router, which have been mentioned on irc is removing UP kernel support;
this needs SMP kernel support on all systems, and no noticiable performance diff IMO)