Fix multicast filtering on STM32

[multiplemonomials]

Summary of changes

This PR fixes two issues with Ethernet multicast filtering on STM32. It's an update to my previous PR which added mcast filtering, but which I wasn't able to easily test the final version of (so some issues slipped through :( )

Issue 1: Hash table registers were swapped, meaning filtering wouldn't work once the perfect filter registers filled up

Issue 2: STM32 Eth IP v1 targets were calling HAL_ETH_ConfigMAC() after the point where I enabled mcast filtering, causing the register settings to get erased and all multicasts to be accepted regardless of filtering.

Impact of changes

Multicast filtering should actually work on STM32 targets now!

Migration actions required

Documentation

None

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Pull request type

[X] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)

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Test results

[] No Tests required for this change (E.g docs only update)
[] Covered by existing mbed-os tests (Greentea or Unittest)
[X] Tests / results supplied as part of this PR

Tested using the emac test on STM32F4, it passed!