bug#38796: 26.3; `view-lossage': Use a variable for the lossage limit

[Tino Calancha]

On Sat, 27 Jun 2020, Eli Zaretskii wrote:

> My personal view is that we should allow only growing the size and
> resetting it to the original size of 300.  Disabling the key record
> should be a separate feature, most probably implemented by means other
> than shrinking the recent_keys vector.

I totally agree: they are clearly 2 separated features.

Thanks for the comments, I will work on them and get back once
completed and tested.