ui: Condition UI-string "channel" terminology on >=255, not >255

[chrisbobbe]

Oops; this was missed because I didn't do end-to-end testing before we merged #5830.

[gnprice]

Thanks! Looks good; merging.

I also did some greps for other places where we compare a feature level, and I think we have them all the right way around.

In particular non-strict inequalities are now all "current feature level >= threshold", and strict inequalities are all "<", from reading the output of:

$ git grep 'eatureLevel.*(?<!=)[><]=' 
$ git grep 'eatureLevel.*(?<!=)[><](?!=)' 

and for good measure:

$ git grep '(?<!=)[><]=.*eatureLevel' 
$ git grep '(?<!=)[><](?!=).*eatureLevel'