[network] fixes Ethernet default config/validation, minor optimizations

[avtolstoy]

Problem

PIN_INVALID should not be used as a default pin setting for wiznet config. It's very easy to put ethernet driver into a not so performant mode due to lack of interrupt pin configuration.

Solution

PIN_INVALID should not be used to reset the settings, as currently calling

        if_wiznet_pin_remap remap = {};
        remap.base.type = IF_WIZNET_DRIVER_SPECIFIC_PIN_REMAP;

        remap.cs_pin = PIN_INVALID; // default
        remap.reset_pin = PIN_INVALID; // default
        remap.int_pin = PIN_INVALID; // default

        auto ret = if_request(nullptr, IF_REQ_DRIVER_SPECIFIC, &remap, sizeof(remap), nullptr);

will result in cs_pin being properly overridden to defaults, but not RESET or INT. This is not in public docs, but a couple of test apps are using this.

Reset to defaults should be:

        if_wiznet_pin_remap remap = {};
        remap.base.type = IF_WIZNET_DRIVER_SPECIFIC_PIN_REMAP;

        remap.cs_pin = HAL_PLATFORM_ETHERNET_WIZNETIF_CS_PIN_DEFAULT; // default
        remap.reset_pin = HAL_PLATFORM_ETHERNET_WIZNETIF_RESET_PIN_DEFAULT; // default
        remap.int_pin = HAL_PLATFORM_ETHERNET_WIZNETIF_INT_PIN_DEFAULT; // default

        auto ret = if_request(nullptr, IF_REQ_DRIVER_SPECIFIC, &remap, sizeof(remap), nullptr);

until we introduce a nicer API.

When loading the config from filesystem, if we see cs_pin = PIN_INVALID - invalidate the whole config to the defaults. This is NOT a valid configuration and it's better to just revert to defaults.

Setting reset_pin or int_pin to PIN_INVALID is still allowed.

This PR also includes some minor optimizations to ethernet driver itself.

Steps to Test

N/A

Example App

N/A

References

Links to the Community, Docs, Other Issues, etc..

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Completeness

• User is totes amazing for contributing!
• Contributor has signed CLA (Info here)
• Problem and Solution clearly stated
• Run unit/integration/application tests on device
• Added documentation
• Added to CHANGELOG.md after merging (add links to docs and issues)