Ondřej Surý authored Feb 01, 2020 and Mark Andrews committed Feb 05, 2020

Found by LGTM.com (see below for description), and while it should not
happen as EDNS OPT RDLEN is uint16_t, the fix is easy.  A little bit
of cleanup is included too.

> In a loop condition, comparison of a value of a narrow type with a value
> of a wide type may result in unexpected behavior if the wider value is
> sufficiently large (or small). This is because the narrower value may
> overflow. This can lead to an infinite loop.