adding a sysctl man section

[John-Mark Gurney]

Inspired by: https://twitter.com/michaeldexter/status/1359614809365311490

I realized that we could/should create a new sysctl section.  My initial
thought was section s, but I'd be open for other recommendations.

Then, any page that describes a sysctl, would add an MLINK to it:
MLINK+= xhci.4 hw.usb.xhci.debug.s

This section would be added to the default search, and then users
would simply be able to type: man <sysctl> and get directed to the
page that has information about it.

Any objections?

-- 
  John-Mark Gurney				Voice: +1 415 225 5579

     "All that I will do, has been done, All that I have, has not."