smoketest: T4576: add guard timeout for systemd in log level tests (backport #4129)

[mergify]

Change Summary

Systemd comes with a default of 5 restarts in 10 seconds policy, this limit can be hit by this reastart sequence, slow down a bit.

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/T4576

Related PR(s)

• T4576: Accel-ppp logging level configuration #3510

Component(s) name

Smoketest

Smoketest result

$ /usr/libexec/vyos/tests/smoke/cli/test_vpn_l2tp.py
test_accel_ipv4_pool (__main__.TestVPNL2TPServer.test_accel_ipv4_pool) ... ok
test_accel_ipv6_pool (__main__.TestVPNL2TPServer.test_accel_ipv6_pool) ... ok
test_accel_limits (__main__.TestVPNL2TPServer.test_accel_limits) ... ok
test_accel_local_authentication (__main__.TestVPNL2TPServer.test_accel_local_authentication) ... ok
test_accel_log_level (__main__.TestVPNL2TPServer.test_accel_log_level) ... ok
test_accel_name_servers (__main__.TestVPNL2TPServer.test_accel_name_servers) ... ok
test_accel_next_pool (__main__.TestVPNL2TPServer.test_accel_next_pool) ... ok
test_accel_ppp_options (__main__.TestVPNL2TPServer.test_accel_ppp_options) ... ok
test_accel_radius_authentication (__main__.TestVPNL2TPServer.test_accel_radius_authentication) ... ok
test_accel_shaper (__main__.TestVPNL2TPServer.test_accel_shaper) ... ok
test_accel_snmp (__main__.TestVPNL2TPServer.test_accel_snmp) ... ok
test_accel_wins_server (__main__.TestVPNL2TPServer.test_accel_wins_server) ... ok
test_l2tp_radius_server (__main__.TestVPNL2TPServer.test_l2tp_radius_server) ... ok
test_l2tp_server_authentication_protocols (__main__.TestVPNL2TPServer.test_l2tp_server_authentication_protocols) ... ok
test_vpn_l2tp_dependence_ipsec_swanctl (__main__.TestVPNL2TPServer.test_vpn_l2tp_dependence_ipsec_swanctl) ... ok

----------------------------------------------------------------------
Ran 15 tests in 89.482s

OK

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

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This is an automatic backport of pull request #4129 done by [Mergify](https://mergify.com).

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