use is_power_of_two where appropriate

test-cargo-miri/tests/test.rs

@@ -68,7 +68,7 @@ fn page_size() {
 
     // In particular, this checks that it is not 0.
     assert!(
-        page_size.next_power_of_two() == page_size,
+        page_size.is_power_of_two(),
         "page size not a power of two: {}",
         page_size
     );