[connman] Prevent IPv4 only VPN data and DNS leak to IPv6. Fixes JB#48769
When IPv4 only VPN is connected IPv6 must be disabled either on the system level when there can be multiple connected techs to avoid data/DNS leak to the IPv6 in case the DNS server of the VPN returns a reply to an AAAA request. In case there is only one connected technology it is enough to disable IPv6 on that but in order to be effective the accept_ra and autoconf needs to be set off as well. Otherwise the RA will bring the interface up, and it will in this case get up momentarily for RA/RS with a LL address to handle the data - but only permanently without configuring the global address.
Split routing change also does need to change the IPv6 state when the value changes.
This does remove a lot of VPN dependency code from service.c to be replaced with usage of the service ident from
plugins/vpn.c for sorting the service list with VPN transports in order to ensure the same functionality as before.
dnsproxy.c has fix for enabling the DNS servers of the split routed VPN when value change happens when connected.
Also a lot of fixes from upstream are included to address RA/RS timings and ipconfig usage in service.c.