Make single onion service to rend and Tor2web to intro link authentication into a protocol warning

Single onion services and Tor2web connect directly to relays using untrusted link authentication keys.

These connections can cause a lot of warnings, particularly due to the link auth bugs in legacy/trac#26627 (moved).

We can either:

downgrade all link auth warnings to protocol warnings on single onion services and Tor2web (this is the fast fix)
taint untrusted link auth keys, and then downgrade connections using tainted keys to protocol warnings (this is very intrusive)

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