use #if instead of #ifdef for HAVE_DECL_IPV6_V6ONLY (continued)
use #if instead of #ifdef for HAVE_DECL_IPV6_V6ONLY (continued)

In 2f4cafdc not all occurences were changed

jspahrsummers/network,iquiw/network,Mikehunan/network,iquiw/network,Mikehunan/network