nanostack: icmpv6: fix build warning

[naveenkaje]

Description

Fix the following build warning seen when building with GCC

Compile [ 54.2%]: icmpv6.c
[Warning] icmpv6.c@1091,16: this statement may fall through [-Wimplicit-fallthrough=]

Pull request type

[x] Fix
[ ] Refactor
[ ] Target update
[ ] Functionality change
[ ] Docs update
[ ] Test update
[ ] Breaking change

[ciarmcom]

@naveenkaje, thank you for your changes.
@ARMmbed/mbed-os-mesh @ARMmbed/mbed-os-maintainers please review.

[ciarmcom]

@naveenkaje, thank you for your changes.
@ARMmbed/mbed-os-mesh @ARMmbed/mbed-os-maintainers please review.

[cmonr]

CI started while waiting on Mesh Team.

Not too conmfortable simply ignoring a warning, but if only GCC is complainging, it can't be that bad?

[mbed-ci]

Test run: FAILED

Summary: 2 of 8 test jobs failed
Build number : 1
Build artifacts

Failed test jobs:

• jenkins-ci/mbed-os-ci_build-ARMC6
• jenkins-ci/mbed-os-ci_build-GCC_ARM

[0xc0170]

100644 → 100755

Fix file attributes.

attribute ((fallthrough));

Failing few builds, is this available in all our toolchains?

[naveenkaje]

100644 → 100755

Fix file attributes.

attribute ((fallthrough));

Failing few builds, is this available in all our toolchains?

I see

[Warning] icmpv6.c@1087,0:  #1207-D: unknown attribute "fallthrough"
[Warning] icmpv6.c@1096,0:  #1207-D: unknown attribute "fallthrough"

With ARMCC. Perhaps it is only for GCC.

https://gcc.gnu.org/onlinedocs/gcc/Warning-Options.html indicates that this is standardized now. I changed my patch and tested with ARMCC and GCC. I see no warnings locally. Lets see if this is ok for all supported toolchains in our CI.

Attribute updated.

[cmonr]

CI started

[mbed-ci]

Test run: SUCCESS

Summary: 12 of 12 test jobs passed
Build number : 2
Build artifacts