Currently, we're trying to export the IPv6 modules from netsyms.c,
which can't work when netsyms is built-in, but IPv6 is modular. Fix is to
move the IPv6 symbols to the ipv6 module. Actually, netsyms.c could use a
lot more of this kind of untangling.

Also, move exporting the secure_*v6* symbols to drivers/char/random.c, 
since that's where they're defined.

The reason why things worked before is that the ipv6 module doesn't have
a EXPORT_NO_SYMBOLS directive, so _all_ of its symbols where exported by
modutils.