Revert EDNS0Record to a trivial type

Revert EDNS0Record to a trivial type

Adding brace initializers makes it non-trivial, which does not seem
like a very good idea for a packed structure.
gcc 8.1.0 complains with:

```
warning: ‘void* memcpy(void*, const void*, size_t)’ copying an object of non-trivial type ‘struct EDNS0Record’ from an array of ‘uint32_t’ {aka ‘unsigned int’} [-Wclass-memaccess]
         memcpy(&stuff, &ttl, sizeof(stuff));
```