ipv6cp: Fix ipv6cp-accept-local and ipv6cp-accept-remote options (#282)
These options are completely broken and ignored because pppd reflects these
options in the incorrect struct ipv6cp_allowoptions. Instead pppd expects
that these options are reflected in struct ipv6cp_wantoptions. Same applies
also for IPv4 code where these options are reflected in struct wantoptions.
This issue can be tested and verified by following command:
First pppd prefer to use IPv6 addresses ::2 and ::1 but accept also any
address suggested by second pppd. Second pppd allows usage only of IPv6
addresses ::1:1 and ::1:2 and does not accept any suggestion by first pppd.