[IPv6] Fix coverity

[ActoryOu]

[IPv6] Fix coverity

Description

Fix coverity violations introduced recently.

• DEADCODE in FreeRTOS_Routing.c line 824-838.
• MISRA C-2012 Rule 10.4 in FreeRTOS_RA.c line 270.
• MISRA C-2012 Rule 10.8 in FreeRTOS_IP_Utils.c line 433.
• MISRA C-2012 Rule 11.3 in FreeRTOS_TCP_State_Handling_IPV4.c line 88-90.
• MISRA C-2012 Rule 11.9 in FreeRTOS_Routing.c line 743.
• MISRA C-2012 Rule 14.2 in FreeRTOS_ND.c line 237.
• MISRA C-2012 Rule 17.2 in FreeRTOS_Sockets.c line 4636-4639.
• MISRA C-2012 Rule 21.6 in FreeRTOS_Routing.c line 1522-1524.
• MISRA C-2012 Rule 8.13 in:
  • FreeRTOS_TCP_Utils_IPV6.c line 66.
  • FreeRTOS_ARP.c line 479.
• MISRA C-2012 Rule 9.2 in FreeRTOS_DNS_Cache.c line 54 + FreeRTOS_IP.c line 530-535.
• MISRA C-2012 Rule 9.3 in FreeRTOS_Routing.c line 743-744.
• MISRA C-2012 Rule 11.3 in FreeRTOS_ARP.c line 1471.
• MISRA C-2012 Rule 15.7 inFreeRTOS_DHCPv6.c line 354.

Test Steps

cov-configure --force --compiler cc --comptype gcc  -- -m32 -std=gnu90

cmake -B build -S test/Coverity

cd build/
cp ../test/Coverity/coverity_misra.config .

cov-build --emit-complementary-info --dir cov-out make

cd cov-out/
cov-analyze --dir . --coding-standard-config ../coverity_misra.config --tu-pattern "file('.*/FreeRTOS-Plus-TCP/source/.*')"

cov-format-errors --dir . --exclude-files '(.*/FreeRTOS-Kernel/.*)' --html-output html-output

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

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[moninom1]

I think we decided not to do these kind of declaration. @tony-josi-aws to take a look.

[ActoryOu]

This is detected as DEADCODE by Coverity. xIsIPv6 is set to either pdTRUE or pdFALSE in the top of this function. It's impossible to enter default case when IPv4/IPv6 are both enabled (which we use in coverity scanning). But it's still possible in differnt configuration (for example, IPv4 only). So we need to keep it in the code.

[tony-josi-aws]

I think the only alternative is to take a MISRA exception here, but I believe this looks better than taking exception.