Revert r274200. Implicitly setting DEBUG_FLAGS when WITH_CTF is true is
not the right way to do this.

Requested by:	kan
Remove ip6_getdstifaddr() and all functions to work with auxiliary data.
It isn't safe to keep unreferenced ifaddrs. Use in6ifa_ifwithaddr() to
determine ifaddr corresponding to destination address. Since currently
we keep addresses with embedded scope zone, in6ifa_ifwithaddr is called
with zero zoneid and marked with XXX.

Also remove route and lle lookups from ip6_input. Use in6ifa_ifwithaddr()
instead.

Sponsored by:	Yandex LLC
Merge remote-tracking branch 'freebsd/master' into hardened/current/master