Add common packet filtering and use it in the STM32 interface

[HTRamsey]

Description

When ipconfigETHERNET_DRIVER_FILTERS_PACKETS is enabled, network drivers must perform IP admission checks before handing packets to the IP task. The STM32 interface currently contains an unimplemented packet-filter hook.

Add eConsiderPacketForProcessing() to validate received descriptors and dispatch shared IPv4/IPv6 header and address checks. Extract those rules from the existing IP-task paths so fixes apply consistently to both filtering configurations, while preserving their existing loopback behavior. Checksum and transport processing remain in their existing paths.

Update STM32 to call the helper after the completed descriptor has its received length and matching endpoint. Remove its placeholder protocol checks, require fixed protocol headers before endpoint lookup, and avoid posting an empty RX event when every packet in a batch is rejected.

Test Steps

• Added dispatcher unit tests for invalid descriptors, truncated headers, address-family mismatches, ARP/custom frames, and IPv4/IPv6 policy delegation.
• Passed six unit suites: FreeRTOS_IP_DiffConfig3, FreeRTOS_IPv4, FreeRTOS_IPv4_DiffConfig, FreeRTOS_IPv4_DiffConfig1, FreeRTOS_IPv6, and FreeRTOS_IPv6_ConfigDriverCheckChecksum.
• Passed eight CMake build configurations: ENABLE_ALL, ENABLE_ALL_IPV4, ENABLE_ALL_IPV6, ENABLE_ALL_IPV4_TCP, ENABLE_ALL_IPV6_TCP, ENABLE_ALL_IPV4_IPV6, DISABLE_ALL, and DEFAULT_CONF, using the host loopback interface.
• Compiled STM32 F4/F7/H5/H7 receive integration with packet filtering and linked RX messages independently enabled/disabled (16 combinations). Existing unused-parameter/variable warnings were suppressed.
• Supplemental temporary host checks passed RX callback/input ordering, rejected-buffer release, empty-batch handling, and minimum header lengths in all four filtering/linked-RX configurations.
• git diff --check passed. STM32 hardware validation was not performed.

Checklist:

• I have tested my changes. No regression in existing tests.
• I have modified and/or added unit-tests to cover the code changes in this Pull Request.

Related Issue

No linked issue.

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