golangci: add new-from-rev flag

This flag allows to run linters only on the files changed since the
given revision. Since we can assume that the code adheres to linting
standards before said revision, this ensures that new code adheres to
the aditional restrictions from `lll`.

.golangci.yml

@@ -73,3 +73,4 @@ issues:
         - unused
         - deadcode
         - varcheck
+  new-from-rev: c118c9095a3175d1d311fa9bf6555b44aa8d3912