fix 6 year old bug in ipaddress.h

[Rotzbua]

This bug causes multiple sram usage. Now only one instance should be in sram.

fix arduino/Arduino#1007

[matthijskooijman]

I wonder if this would be better fixed by making the declaration in the .h file constexpr and give it a value there. I believe that, to allow taking the address of the constant, it still needs a definition in the .cpp file as introduced by this PR, but then the definition does not need to assign a value.

[facchinm]

Fixed by arduino/ArduinoCore-API@3dbd7d7 (as soon as AVR core will be based on chainsaw the patch will be applied here as well)

[aentinger]

Closing this issue since initial port of Arduino API has been done and this issue is fixed with arduino/ArduinoCore-API@3dbd7d7 as noted by @facchinm .