sonic.c: Fix warning on gcc 6
GCC 6.0 previews give the following warning on sonic.c:
../../../../../rtems/c/src/libchip/network/sonic.c:837:11: warning: statement is indented as if it were guarded by... [-Wmisleading-indentation]
This was discussed here:
https://lists.rtems.org/pipermail/devel/2016-March/014004.html
and we concluded it would be better to rewrite the entire snippet.