netdisco-do overrides `_min_age` config
netdisco-do overrides `_min_age` config

Give the user wanting to manually run a discover|arpnip|macsuck job in
the foreground preference over the respective `_min_age` setting. Tiny
quality of life improvement that mostly comes up in debugging.

netdisco/netdisco,netdisco/netdisco,netdisco/netdisco