DNS-over-TLS should use "dot" ALPN
During connection establishment the Application-Layer Protocol Negotiation (ALPN) token "dot" [DoT-ALPN] MUST be selected in the TLS handshake.
Thus, we should just use
dot as ALPN for all DoT connections as it is registered as ALPN for DoT.
This issue is a part of #2775 (closed).