fix(iroh-relay): Report round-trip-latency instead of single-trip for QAD (#3230)

## Description

Switches QAD latency to be round-trip instead of single-trip to match
STUN latencies.

## Notes & open questions

Fixes #3225

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## Change checklist
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- [x] Self-review.

Author: matheus23

iroh-relay/src/quic.rs

@@ -273,7 +273,7 @@ impl QuicClient {
         // if we've sent to an ipv4 address, but received an observed address
         // that is ivp6 then the address is an [IPv4-Mapped IPv6 Addresses](https://doc.rust-lang.org/beta/std/net/struct.Ipv6Addr.html#ipv4-mapped-ipv6-addresses)
         observed_addr = SocketAddr::new(observed_addr.ip().to_canonical(), observed_addr.port());
-        let latency = conn.rtt() / 2;
+        let latency = conn.rtt();
         // gracefully close the connections
         conn.close(QUIC_ADDR_DISC_CLOSE_CODE, QUIC_ADDR_DISC_CLOSE_REASON);
         Ok((observed_addr, latency))