drivers: ethernet: eth_stm32_hal allow proper priority assignment to rx_thread

[clamattia]

Describe the bug
#77904 introduced the defect of coupling the cooperativeness of the driver-thread to the cooperativeness of the traffic-class queue.

It makes sense for an application to assign different cooperativenesses to these.

@descsny has already suggested in above PR to not couples those two priorities. Coupling the two priority cooperativeness levels is too restrictive.

To Reproduce
NA

Expected behavior
Please do as suggested by #77904 (comment)

Impact
Proper priorities can no longer be assigned.

Logs and console output
NA

Environment (please complete the following information):
NA

Additional context
NA

[henrikbrixandersen]

Please use our bug template when reporting bugs. You need to edit this issue to include the information requested in https://github.com/zephyrproject-rtos/zephyr/blob/main/.github/ISSUE_TEMPLATE/001_bug_report.md

[clamattia]

Please use our bug template when reporting bugs. You need to edit this issue to include the information requested in https://github.com/zephyrproject-rtos/zephyr/blob/main/.github/ISSUE_TEMPLATE/001_bug_report.md

@henrikbrixandersen Thank you. I hope it fits better now.

[clamattia]

Le me know, if this is considered an enhancement, and I am happy to adjust the wording.