Apart from advancing the buffer by RR_TYPE_LENGTH, RR_CLASS_LENGTH,
and RR_TTL_LENGTH the code also attempts to read a two byte unsigned
integer using _get_short(bufpos):
unsigned addrlen = ntohs(_get_short(bufpos));
The bounds check must therefore ensure that the given buffer is large
enough to contain two more bytes after advancing the buffer.
Saving RAM is more important than saving a few cycles
used by re-creating the request buffer in the error case.
Also reduce the size of the buffer to 128 bytes.
If we are just requesting the AAAA record it is unlikely
for the reply to take up the maximum size of 512 bytes.
We were already placing restrictions on the domain name length,
those are now actually a bit more relaxed (112 bytes instead of 64)
