Pass on default value of radstep in make_edi

This is a bugfix for make_edi when -radfix is chosen. Problem was:
if the user did not specify -radstep, then the default value of 0
was not written to the sam.edi output file. Now it is. Also
renamed "radfix" variable to "radstep" because that better reflects
what it is.

Change-Id: I0cc6ee84d42b18ee0ea6b045cdfb0c1d55d51b9f