MINOR: quic: Add a trace to identify connections which sent Initial packet.

This should help in diagnosing issues revealed by the interop runner which counts
the number of handshakes from the number of Initial packets sent by the server.

Must be backported to 2.7.

src/quic_conn.c

@@ -632,6 +632,11 @@ static void quic_trace(enum trace_level level, uint64_t mask, const struct trace
 					chunk_appendf(&trace_buf, " frm@%p", frm);
 					chunk_frm_appendf(&trace_buf, frm);
 				}
+
+				if (pkt->type == QUIC_PACKET_TYPE_INITIAL) {
+					chunk_appendf(&trace_buf, " with scid");
+					quic_cid_dump(&trace_buf, &qc->scid);
+				}
 			}
 		}