example: Use "Total SNR", not "GSNR"

Various presentations from Polito are slowly changing to use "GSNR" as a
"Generalized SNR", but it's true that our code does not use this term
anywhere, and that it is not properly explained. Let's wait a bit for
this term to become a bit more mainstream and for updated docs on our
side; then this commit can be safely reverted.

Thanks to Jonas for reporting this.

examples/transmission_main_example.py

@@ -161,7 +161,7 @@ def main(network, equipment, source, destination, sim_params, req=None):
             print(f'\nTransmission result for input power = {lin2db(req.power*1e3):.2f} dBm:')
         else:
             print(f'\nTransmission results:')
-        print(f'  Final GSNR (signal bw): {ansi_escapes.cyan}{mean(destination.snr):.02f} dB{ansi_escapes.reset}')
+        print(f'  Final SNR total (signal bw): {ansi_escapes.cyan}{mean(destination.snr):.02f} dB{ansi_escapes.reset}')
 
         #print(f'\n !!!!!!!!!!!!!!!!!     TEST POINT         !!!!!!!!!!!!!!!!!!!!!')
         #print(f'carriers ase output of {path[1]} =\n {list(path[1].carriers("out", "nli"))}')