T4971: Accel-ppp verify if client_ip_pool key exists in config

[sever-sever]

Change Summary

If client_ip_pool not exists in the config we cannot search for it in the dictionary
dict_search_recursive(config, 'gateway_address', ['client_ip_pool', 'name'])
Add check

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe):

Related Task(s)

• https://vyos.dev/T4971

Component(s) name

pppoe-server

Proposed changes

How to test

VyOS config:

set service pppoe-server authentication mode 'radius'
set service pppoe-server authentication radius server 192.168.122.14 key 'vyos-secret'
set service pppoe-server interface eth1

Before fix:

Traceback (most recent call last):
  File "/usr/libexec/vyos/conf_mode/service_pppoe-server.py", line 116, in <module>
    verify(c)
  File "/usr/libexec/vyos/conf_mode/service_pppoe-server.py", line 62, in verify
    verify_accel_ppp_base_service(pppoe)
  File "/usr/lib/python3/dist-packages/vyos/configverify.py", line 424, in verify_accel_ppp_base_service
    for _, v in config['client_ip_pool']['name'].items():
KeyError: 'client_ip_pool'



[[service pppoe-server]] failed
Commit failed
[edit]
vyos@r14#

After fix (expected failed as gateway is not configured):

vyos@r14# commit
[ service pppoe-server ]
Server requires gateway-address to be configured!

[[service pppoe-server]] failed
Commit failed
[edit]
vyos@r14# 

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• I have run the components SMOKETESTS if applicable
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly