ck_hs: Re-order map elements according to reader use.

Try to get generation, probe_maximum, mask and step on same
cache line.

src/ck_hs.c

@@ -50,13 +50,13 @@
 
 struct ck_hs_map {
 	unsigned int generation[CK_HS_G];
-	unsigned int tombstones;
 	unsigned int probe_maximum;
+	unsigned long mask;
+	unsigned long step;
 	unsigned int probe_limit;
+	unsigned int tombstones;
 	unsigned long n_entries;
-	unsigned long mask;
 	unsigned long capacity;
-	unsigned long step;
 	unsigned long size;
 	void **entries;
 };