Do define some IPv6 related symbols even with IPv6 disabled
Do define some IPv6 related symbols even with IPv6 disabled

Fixes compilation of some faulty applictions.
Patch from Freetz.org

Reported-by: Leonid Lisovskiy <66c38905dfb44479707f7ccea5c07862e8cf461c@gmail.com>

brgl/uclibc-ng,foss-for-synopsys-dwc-arc-processors/uClibc,brgl/uclibc-ng,kraj/uclibc-ng,kraj/uclibc-ng,wbx-github/uclibc-ng,brgl/uclibc-ng,wbx-github/uclibc-ng,foss-for-synopsys-dwc-arc-processors/uClibc,brgl/uclibc-ng,foss-for-synopsys-dwc-arc-processors/uClibc,kraj/uclibc-ng,wbx-github/uclibc-ng,wbx-github/uclibc-ng,foss-for-synopsys-dwc-arc-processors/uClibc,kraj/uclibc-ng