pppoe: T4384: replace default-route CLI option with common CLI nodes already present for DHCP

VyOS 1.4 still leverages PPPd internals on the CLI.

pppd supports three options for a default route, none, auto, force.
* none: No default route is installed on interface up
* auto: Default route is only installed if there is yet no default route
* force: overwrite any default route

There are several drawbacks in this design for VyOS and the users. If auto is
specified, this only counted for static default routes - but what about dynamic
ones? Same for force, only a static default route got replaced but dynamic ones
did not got taken into account.

The CLI is changed and we now re-use already existing nodes from the DHCP
interface configuration:
* no-default-route:
  On link up no default route is installed, same as the previous
  default-route none

* default-route-distance:
  We can now specify the distance of this route for the routing table on the
  system. This defaults to 210 as we have for DHCP interfaces. All this will be
  migrated using a CLI migration script.

1 files changed, 54 insertions, 0 deletions

diff --git a/src/migration-scripts/interfaces/25-to-26 b/src/migration-scripts/interfaces/25-to-26
new file mode 100755
index 000000000..a8936235e
--- /dev/null
+++ b/src/migration-scripts/interfaces/25-to-26
@@ -0,0 +1,54 @@
+#!/usr/bin/env python3
+#
+# Copyright (C) 2022 VyOS maintainers and contributors
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License version 2 or later as
+# published by the Free Software Foundation.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+# T4384: pppoe: replace default-route CLI option with common CLI nodes already
+#        present for DHCP
+
+from sys import argv
+
+from vyos.ethtool import Ethtool
+from vyos.configtree import ConfigTree
+
+if (len(argv) < 1):
+    print("Must specify file name!")
+    exit(1)
+
+file_name = argv[1]
+with open(file_name, 'r') as f:
+    config_file = f.read()
+
+base = ['interfaces', 'pppoe']
+config = ConfigTree(config_file)
+
+if not config.exists(base):
+    exit(0)
+
+for ifname in config.list_nodes(base):
+    tmp_config = base + [ifname, 'default-route']
+    if config.exists(tmp_config):
+        # Retrieve current config value
+        value = config.return_value(tmp_config)
+        # Delete old Config node
+        config.delete(tmp_config)
+        if value == 'none':
+            config.set(base + [ifname, 'no-default-route'])
+
+try:
+    with open(file_name, 'w') as f:
+        f.write(config.to_string())
+except OSError as e:
+    print(f'Failed to save the modified config: {e}')
+    exit(1)