MINOR: quic: Comment fix about the token found in Initial packets

Mention that the token is sent only by servers in both server and listener
packet parsers.
Remove a "TO DO" section in listener packet parser because there is nothing
more to do in this function about the token
diff --git a/src/xprt_quic.c b/src/xprt_quic.c
index d021f62..8a9b4f2 100644
--- a/src/xprt_quic.c
+++ b/src/xprt_quic.c
@@ -3942,7 +3942,8 @@
 			 * So, a client which receives an Initial packet with a token
 			 * MUST discard the packet or generate a connection error with
 			 * PROTOCOL_VIOLATION as type.
-			 * The token must be provided in a Retry packet or NEW_TOKEN frame.
+			 * The token may be provided in a Retry packet or NEW_TOKEN frame
+			 * only by the QUIC server.
 			 */
 			pkt->token_len = token_len;
 		}
@@ -4429,12 +4430,8 @@
 				goto err;
 			}
 
-			/* XXX TO DO XXX 0 value means "the token is not present".
-			 * A server which sends an Initial packet must not set the token.
-			 * So, a client which receives an Initial packet with a token
-			 * MUST discard the packet or generate a connection error with
-			 * PROTOCOL_VIOLATION as type.
-			 * The token must be provided in a Retry packet or NEW_TOKEN frame.
+			/* The token may be provided in a Retry packet or NEW_TOKEN frame
+			 * only by the QUIC server.
 			 */
 			pkt->token_len = token_len;