ISDN: Export "kstat"

This patch exports the kstat per-cpu variable, needed for
hisax, which uses kstat_irqs() during card probing to make sure
that irqs actually work. This could possibly replaced by a
private counter in the hisax ISRs, but that's really just
unnecessary overhead, since the core kernel already does the work
anyway.

kernel/sched.c

@@ -1151,6 +1151,8 @@ static inline void rebalance_tick(runqueue_t *this_rq, int idle)
 
 DEFINE_PER_CPU(struct kernel_stat, kstat) = { { 0 } };
 
+EXPORT_PER_CPU_SYMBOL(kstat);
+
 /*
  * We place interactive tasks back into the active array, if possible.
  *