get rid of ifconfig

Ifconfig is no longer installed on Fedora (no wonder since it's obsolete already for 20 years) so it might not be present on other distros as well in near future. We should replace it either with ip or with some steps for the repeated checks).

The ifconfig is used 37 times, of that 3 times in lib/ and there is one step based on ifconfig (which is used twice). The rest are direct calls, mostly "{pattern}" is [not] visible with "ifconfig ...".

(ip in is visible with command "ip is used 1568-times for more diverse stuff than just ifconfig so I'd probably go with just ifconfig replacement.)