Revert "Removing AF_INET6_FREEBSD, already defined in bits/socket.h"

This reverts commit 7ed2998609b05a58cc2efb159cfcf5621c8606ca.
Revert "Removed old AF_INET6_* defines"

This reverts commit fce7ffbb1bd0995229b41f62324e64eaf81dafce.