userguide: fix explanation about bsize ranges

userguide: fix explanation about bsize ranges

Our code handles Uint ranges as exclusive, but for bsize, our
documentation stated that they're inclusive.

Cf. from uint.rs:

    DetectUintMode::DetectUintModeRange => {
        if val > x.arg1 && val < x.arg2 {
            return true;
        }
    }

Task #6708

(cherry picked from commit 244a35d539989c00eb5cbac86e7355227cd9da03)