Check dynamics of Nafx.mod

[sanjayankur31]

[HengyeZhu]

When I run nafx.mod in NEURON Simulator, the value of stau is abnormal: theoretically, when stau < taumin (30 ms), stau should be 30 ms. However, during the actual run, stau remains constantly at 0. I did some debugging and found that even when I explicitly define stau=30 in the procedure, stau still remains constantly at 0.

This issue was not found in NeuroML2, but I'm not sure which one is correct.