Don't panic if we fail to satisfy an M_WAITOK request; return 0 instead.

The calling code will either handle that gracefully or cause a page fault.

sys/vm/vm_kern.c

@@ -336,9 +336,11 @@ kmem_malloc(map, size, flags)
 			}
 			return (0);
 		}
+#if 0
 		if ((flags & M_NOWAIT) == 0)
 			panic("kmem_malloc(%ld): kmem_map too small: %ld total allocated",
 				(long)size, (long)map->size);
+#endif
 		return (0);
 	}
 	offset = addr - VM_MIN_KERNEL_ADDRESS;