MINOR: quic: Comment fix.

When we drop a packet with unknown length, this is the entire datagram which
must be skipped.
diff --git a/src/xprt_quic.c b/src/xprt_quic.c
index 9ab675c..3ba009f 100644
--- a/src/xprt_quic.c
+++ b/src/xprt_quic.c
@@ -4259,7 +4259,7 @@
 	return pkt->len;
 
  err:
-	/* If length not found, consume the entire packet */
+	/* If length not found, consume the entire datagram */
 	if (!pkt->len)
 		pkt->len = end - beg;
 	TRACE_DEVEL("Leaving in error", QUIC_EV_CONN_LPKT,