Replace 'xMDNS_MACAddressIPv6' with 'xMDNS_MacAddressIPv6' to increas…

[htibosch]

Replace 'xMDNS_MACAddressIPv6' with 'xMDNS_MacAddressIPv6' to increase uniformity

This PR will make the following change:

     const MACAddress_t xLLMNR_MacAddress;
     const MACAddress_t xLLMNR_MacAddressIPv6;
     const MACAddress_t xMDNS_MacAddress;
-    const MACAddress_t xMDNS_MACAddressIPv6;
+    const MACAddress_t xMDNS_MacAddressIPv6;

for the sake of uniformity.
A define will be added to make this change "backward compatible":

/* This type-name was formally "misspelled" as
 * xMDNS_MACAddressIPv6 with "MAC": */
    extern const MACAddress_t xMDNS_MacAddressIPv6;
    /* Guarantee backward compatibility. */
    #define xMDNS_MACAddressIPv6    xMDNS_MacAddressIPv6
#endif /* ipconfigUSE_MDNS */

Test Steps

Enable ipconfigUSE_MDNS and ipconfigUSE_IPv6, and one of these drivers: STM32Hxx, Zynq, or DriverSAM.

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

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[ActoryOu]

Thank you for creating this! Note that this PR is created for #1167.