BUG/MEDIUM: Cur/CumSslConns counters not threadsafe.

CurSslConns inc/dec operations are not threadsafe. The unsigned CurSslConns
counter can wrap to a negative value. So we could notice connection rejects
because of MaxSslConns limit artificially exceeded.

CumSslConns inc operation are also not threadsafe so we could miss
some connections and show inconsistenties values compared to CumConns.

This fix should be backported to v1.8.
1 file changed