discover_fallback_ips() filtered out any DoH-resolved IP that also appeared
in the system resolver's answer set, on the assumption that the system IP
was unreachable. When DoH and system DNS agreed (a common case), the
function returned the hardcoded _SEED_FALLBACK_IPS list instead — and on
networks where those seed addresses are not routable, the Telegram fallback
transport had nothing usable to retry against and polling failed.
Drop the system_ips exclusion so DoH-confirmed IPs are preserved regardless
of system DNS overlap. The TelegramFallbackTransport already tries the
primary path first via system DNS, then falls through to the IP-rewrite
path on connect failure; including the same IP in both lanes lets a
transient primary failure recover via the explicit IP route instead of
escalating to seed addresses.
Update the two tests that codified the old exclusion to reflect the new,
inclusion-by-default behaviour.
Fixes#14520
f6b68f0f50