[bug] Agent crashes when using monitored_interfaces "wlan0 wlan1 br-lan"

[nemesifier]

How to reproduce the bug:

• configure monitored_interfaces to be something like wlan0 wlan1 lan1 lan2 lan3 eth0 wan, eg:

config monitoring 'monitoring'
        option interval '300'
        option verbose_mode '0'
        option required_memory '0.05'
        option max_retries '5'
        option monitored_interfaces 'wlan0 wlan1 lan1 lan2 lan3 eth0 wan mesh0 mesh1'

• restart the agent

Expected outcome: I expected the agent to work normally.

Actual outcome: the agent doesn't start, it gives this error:

Fri Apr 22 20:30:00 2022 daemon.err openwisp-monitoring[23774]: missing required --mode option
Fri Apr 22 20:30:00 2022 daemon.err openwisp-monitoring[23775]: root: No data file found to send.
Fri Apr 22 20:30:05 2022 daemon.err openwisp-monitoring[23802]: missing required --mode option
Fri Apr 22 20:30:10 2022 daemon.err openwisp-monitoring[23803]: missing required --mode option
Fri Apr 22 20:30:15 2022 daemon.err openwisp-monitoring[23804]: missing required --mode option
Fri Apr 22 20:30:20 2022 daemon.err openwisp-monitoring[23834]: missing required --mode option
Fri Apr 22 20:30:26 2022 daemon.err openwisp-monitoring[23843]: missing required --mode option
Fri Apr 22 20:30:26 2022 daemon.info procd: Instance openwisp-monitoring::openwisp-monitoring_collect_data s in a crash loop 6 crashes, 0 seconds since last crash