Always give kalloc's a label

I hadn't realized before that mscan tracks "block" labels and "type" labels separately and prefers type labels over block labels. So, in fact, kalloc's should always be labeled (using block labels) and suballocations from these blocks should also be labeled (using type labels).

Always give kalloc's a label
49def062 · Austin Clements · 0d6716d9 · 49def062 · 49def062
--- a/kernel/kalloc.cc
+++ b/kernel/kalloc.cc
@@ -128,7 +128,6 @@ kmem::alloc(const char* name)
        panic("kmem:alloc: aba race %p %p %p\n",
              r, r->next, nxt);
      nfree--;
-      if (name)
      mtlabel(mtrace_label_block, r, size, name, strlen(name));
      return r;
    }

--- a/kernel/kmalloc.cc
+++ b/kernel/kmalloc.cc
@@ -37,7 +37,7 @@ kminit(void)
 static int
 morecore(int c, int b)
 {
-  char *p = kalloc(nullptr);
+  char *p = kalloc("kmalloc");
  if(p == 0)
    return -1;