EthernetCompat - static IP auto gw,mask,dns as in Arduino libraries

[JAndrassy]

The parameters of begin in EthernetCompat.h are optional but automatic values for gw IP, mask and DNS IP were not calculated.

In the begin(mac, local_ip, arg1), arg1 is assumed to be the DNS IP, because it can be an address outside of the local network. Automatic gw IP based on local_ip with .1 at the end is more likely to be a right auto value than DNS IP. Basically this is the reason for the Arduino ordering of begin parameters.

[d-a-v]

We already have a logic reordering network parameters and it is used in config() which is called just below your proposal.

Did you check if the operations are similar ?

Also, const& are there for IPAddress because IPv6 addresses are more than one single uint32.

[JAndrassy]

this doesn't do a reordering. with no param entered it creates arduino ordering, which is then reordered in the mentioned funtion

IPAddress with IPv6 is not copyable?

[d-a-v]

IPAddress with IPv6 is not copyable?

They are copyable, but when IPv6 is enabled they are bigger than a single reference or a single IPv4.
So it takes less memory / less time to transfer them as constref. It is not a big deal, there are many places where they are passed by copy. In this PR you remove the constref so I explain why they were there: I find it to be a good reason to recall that they can be bigger.

[d-a-v]

this doesn't do a reordering. with no param entered it creates arduino ordering, which is then reordered in the mentioned funtion

OK I misread it.
The goal is to ensure that there is not nothing for IPv4 dns and gateway, by copying static address and setting .1 on the last digit (why not .254?). Out of curiosity is it specified somewhere in their doc or is it only something that is done over many of their implementations from the beginning ?

Why are you not doing this in our global config() (link above) so this arduino logic would spread over all type of interface ?

[JAndrassy]

https://www.arduino.cc/reference/en/libraries/ethernet/ethernet.begin/
these Arduino docs are now imported to the web page from GitHub
https://github.com/arduino-libraries/Ethernet/blob/master/docs/api.md

I am not sure about this in WiFi.config. EthernetCompat is relatively new and aimed to be compatible.
In WiFi.config there is a test for local_ip, gw and dns 0 to return to DHCP. maybe testing local_ip would be enough.

I can prepare a separate PR as an alternative to this PR. There I do the auto values in ipAddressReorder.

[d-a-v]

a step towards API coherence & compatibility
thanks