CW keyer: have the smoother as a class member so it can be controlled by the keyer to determine the ramp length depending on dot length

sdrbase/dsp/cwkeyer.cpp

@@ -197,6 +197,7 @@ void CWKeyer::setWPM(int wpm)
         QMutexLocker mutexLocker(&m_mutex);
         m_dotLength = (int) (0.24f * m_sampleRate * (5.0f / wpm));
         m_wpm = wpm;
+        m_cwSmoother.setNbFadeSamples(m_dotLength/5); // 20% the dot time
     }
 }