Here the Fiber behaviour change because pch = signal + ase + nli is
considered instead of just signal. This slightly changes the
propagation results as more power is considered to be injected in the
fiber span. All differences in tests are below 0.1 dB, with a few
exceptions slightly higher.
Change-Id: I5b2227ee036a26a11e13f3169e16868d70f0c457