Support freebsd (OPNsense etc) for the included plugin isc_dhcpd

[dnlldl]

Support freebsd (OPNsense etc)

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General information

This is to make the isc_dhcpd plugin work with any recent version of OPNsense.

Proposed changes

The dhcpd.leases file is in a different location than expected by the script. The command pidof doesn't exist and awk is also more limited.

root@OPNsense:~ # awk --version
awk version 20210215

This PR could be improved, using a configuration file instead of hardcoding the necessary files would be good. Also, for the pidof problem, which pidof could be used before falling back to something more universal with ps.

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[dnlldl]

is there any chance of this making it in eventually?

[martinhv]

I looked at it and approved it from a product perspective and forward it to a dev for analysis.