config: Refactor the network switch configuration file

This patch prevents the body of the script getting executed when
the script is imported as a module.

Change-Id: I70a50f6295f1e7a088398017f5fa9d06fe90476a
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>

configs/dist/sw.py

@@ -63,6 +63,8 @@ def build_switch(options):
         link.int0 = switch.interface[i]
 
     return switch
+
+def main():
     # Add options
     parser = optparse.OptionParser()
     Options.addCommonOptions(parser)
@@ -73,3 +75,5 @@ system = build_switch(options)
     root = Root(full_system = True, system = system)
     Simulation.run(options, root, None, None)
 
+if __name__ == "__m5_main__":
+    main()