Do define some IPv6 related symbols even with IPv6 disabled

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

Reported-by: Leonid Lisovskiy <lly.dev@gmail.com>

libc/sysdeps/linux/common/bits/in.h

@@ -120,7 +120,7 @@ struct in_pktinfo
   };
 #endif
 
-#ifdef __UCLIBC_HAS_IPV6__
+#if defined __UCLIBC_HAS_IPV6__ || !defined __UCLIBC_STRICT_HEADERS__
 /* Options for use with `getsockopt' and `setsockopt' at the IPv6 level.
    The first word in the comment at the right is the data type used;
    "bool" means a boolean value stored in an `int'.  */