One more change for v3 I think

[Alan DeKok]

  I put a change into master which should probably go into v3, too:

https://github.com/FreeRADIUS/freeradius-server/blob/master/src/main/connection.c#L814

  The connection pool re-uses connections based on “most recently used”.  But the exact definition of MRU is important.  It turns out that “last returned to the pool” is a bad metric.  Because the connection could be blocked / slow.  And re-using that connection would mean re-using a blocked / slow connection.

  The solution is to define MRU as “most recently removed from the pool, and returned to the pool”.  This change prioritizes connections which are fast.

  The code is a bit complicated, because it has to keep track of more information.  But it should result in systems which are more stable.

  Alan DeKok.