Revert "no need to sum stats which we don't use"

my apologies: as long as we pass around a struct wrk, some other
function could use the wrk->stats - in other words, the fact that
the ban stats are decoupled from the wrk stats does not make the
latter any less relevant.

This reverts commit 527f1bd0.

bin/varnishd/cache/cache_ban_lurker.c

@@ -422,6 +422,7 @@ ban_lurker(struct worker *wrk, void *priv)
 		d += VTIM_real();
 		Lck_Lock(&ban_mtx);
 		if (gen == ban_generation) {
+			Pool_Sumstat(wrk);
 			(void)Lck_CondWait(&ban_lurker_cond, &ban_mtx, d);
 			ban_batch = 0;
 		}