Make the key_bits multiple assertion a static_assert

May as well have this fire at compile time.

Make the key_bits multiple assertion a static_assert
1954540a · David Benjamin · 2edf804d · 1954540a
--- a/kernel/radix.cc
+++ b/kernel/radix.cc
@@ -9,8 +9,8 @@ template<class CB>
 void
 descend(u64 key, markptr<void> *n, u32 level, CB cb)
 {
-  // for now, we only support exact multiples of bits_per_level
-  assert(key_bits == bits_per_level * radix_levels);
+  static_assert(key_bits == bits_per_level * radix_levels,
+                "for now, we only support exact multiples of bits_per_level");
  assert(n);

  void *v = n->ptr();