Add macro checks for DNS Cache to fix build issue

[kar-rahul-aws]

Description

This PR addresses the issue for compilation issue when ipconfigUSE_DNS_CACHE is set to 0.

Test Steps

Build FreeRTOS_Plus_TCP_Echo_Posix_Demo .
Before applying the patch

/home/karahulx/FreeRTOS/FreeRTOS-Plus/Source/FreeRTOS-Plus-TCP/source/FreeRTOS_DNS_Parser.c: In function ‘DNS_ReadNameField’:
/home/karahulx/FreeRTOS/FreeRTOS-Plus/Source/FreeRTOS-Plus-TCP/source/FreeRTOS_DNS_Parser.c:104:26: error: ‘ParseSet_t’ {aka ‘struct xParseSet’} has no member named ‘pcName’
  104 |                     pxSet->pcName[ uxNameLen ] = '.';
      |                          ^~
/home/karahulx/FreeRTOS/FreeRTOS-Plus/Source/FreeRTOS-Plus-TCP/source/FreeRTOS_DNS_Parser.c:133:26: error: ‘ParseSet_t’ {aka ‘struct xParseSet’} has no member named ‘pcName’
  133 |                     pxSet->pcName[ uxNameLen ] = ( char ) pucByte[ uxIndex ];
      |                          ^~
/home/karahulx/FreeRTOS/FreeRTOS-Plus/Source/FreeRTOS-Plus-TCP/source/FreeRTOS_DNS_Parser.c:151:26: error: ‘ParseSet_t’ {aka ‘struct xParseSet’} has no member named ‘pcName’
  151 |                     pxSet->pcName[ uxNameLen ] = '\0';
      |                          ^~
/home/karahulx/FreeRTOS/FreeRTOS-Plus/Source/FreeRTOS-Plus-TCP/source/FreeRTOS_DNS_Parser.c: In function ‘DNS_ParseDNSReply’:
/home/karahulx/FreeRTOS/FreeRTOS-Plus/Source/FreeRTOS-Plus-TCP/source/FreeRTOS_DNS_Parser.c:470:94: error: ‘ParseSet_t’ {aka ‘struct xParseSet’} has no member named ‘pcName’
  470 |                             xDNSHookReturn = xApplicationDNSQueryHook_Multi( &xEndPoint, xSet.pcName );
      |                                                                                              ^
/home/karahulx/FreeRTOS/FreeRTOS-Plus/Source/FreeRTOS-Plus-TCP/source/FreeRTOS_DNS_Parser.c: In function ‘parseDNSAnswer’:
/home/karahulx/FreeRTOS/FreeRTOS-Plus/Source/FreeRTOS-Plus-TCP/source/FreeRTOS_DNS_Parser.c:740:65: error: ‘ParseSet_t’ {aka ‘struct xParseSet’} has no member named ‘pcName’
  740 |                             pxNewAddress = pxNew_AddrInfo( pxSet->pcName, FREERTOS_AF_INET6, xIP_Address.xIPAddress.xIP_IPv6.ucBytes );
      |                                                                 ^~
/home/karahulx/FreeRTOS/FreeRTOS-Plus/Source/FreeRTOS-Plus-TCP/source/FreeRTOS_DNS_Parser.c:770:65: error: ‘ParseSet_t’ {aka ‘struct xParseSet’} has no member named ‘pcName’
  770 |                             pxNewAddress = pxNew_AddrInfo( pxSet->pcName, FREERTOS_AF_INET4, ucBytes );
      |                                                                 ^~
make: *** [Makefile:112: build//home/karahulx/FreeRTOS/FreeRTOS-Plus/Source/FreeRTOS-Plus-TCP/source/FreeRTOS_DNS_Parser.o] Error 1

After applying the patch, the project compiles and runs successfully.

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]

Besides, could you add some UT to cover this scenario?

[ActoryOu]

This change forces user to enable CACHE or CALLBACK while using MDNS/LLMNR, which I think is incorrect.

[ActoryOu]

Could you add some more comments in the code to help developers understand why wrapping this is still working if pxNewAddress is NULL when CACHE/CALLBACK are disabled.

[ActoryOu]

Closing because we have #1201 for this issue.