pySim-shell: Add 'switch_channel' command

We've already had the 'open_channel' and 'close_channel' commands,
which were sent to (and acknowledged by) the card.  However,
those commands didn't affect the pySim-shell state, i.e. all
communication would still happen through the default channel '0'.

With this patch we introduce a 'switch_channel' command, using which
the user can determine which of the (previously opened) logical channels
shall be used by pySim-shell.

Change-Id: Ia76eb45c4925882ae6866e50b64d9610bd4d546d
Closes: OS#6230

pySim-shell.py

@@ -963,6 +963,18 @@ class Iso7816Commands(CommandSet):
         # this is executed only in successful case, as unsuccessful raises exception
         self._cmd.rs.del_lchan(opts.chan_nr)
 
+    switch_chan_parser = argparse.ArgumentParser()
+    switch_chan_parser.add_argument(
+        'chan_nr', type=int, default=0, help='Channel Number')
+
+    @cmd2.with_argparser(switch_chan_parser)
+    def do_switch_channel(self, opts):
+        """Switch currently active logical channel."""
+        self._cmd.lchan._select_pre(self._cmd)
+        self._cmd.lchan = self._cmd.rs.lchan[opts.chan_nr]
+        self._cmd.lchan._select_post(self._cmd)
+        self._cmd.update_prompt()
+
     def do_status(self, opts):
         """Perform the STATUS command."""
         fcp_dec = self._cmd.lchan.status()