Move kInvalidPacketNumber to QuicDispatcher: the only place it is used. No behavior change.

net/quic/core/quic_protocol.h

Index: net/quic/core/quic_protocol.h
diff --git a/net/quic/core/quic_protocol.h b/net/quic/core/quic_protocol.h
index 55f396a378d2807071a2dc0c20bd4e3bc87dd470..068ef9a387b034a6ac134dd2686979ce185f1633 100644
--- a/net/quic/core/quic_protocol.h
+++ b/net/quic/core/quic_protocol.h
@@ -100,9 +100,6 @@ struct NET_EXPORT_PRIVATE QuicPacketPublicHeader {
   DiversificationNonce* nonce;
 };
 
-// An integer which cannot be a packet number.
-const QuicPacketNumber kInvalidPacketNumber = 0;
-
 // Header for Data packets.
 struct NET_EXPORT_PRIVATE QuicPacketHeader {
   QuicPacketHeader();