Change IETF Frame/QUIC_VERSION_99 tests to be symbolic.

This CL replaces checks for QUIC_VERSION_99 that are controlling the IETF frames and their associated functionality with a function call . The function has a name that is indicative of the features for which the version is being checked -- VersionHasIetfQuicFrames().

gfe-relnote: N/A just changes the text by which we test if IETF QUIC has been negotiated.
PiperOrigin-RevId: 253767805
Change-Id: I08ae6738411ac151f90d5d085ea69af90d79fb80
diff --git a/quic/core/quic_connection.h b/quic/core/quic_connection.h
index 601dad9..dc97b07 100644
--- a/quic/core/quic_connection.h
+++ b/quic/core/quic_connection.h
@@ -1497,7 +1497,7 @@
   // provided in constructor.
   const bool no_version_negotiation_;
 
-  // Payload of most recently transmitted QUIC_VERSION_99 connectivity
+  // Payload of most recently transmitted IETF QUIC connectivity
   // probe packet (the PATH_CHALLENGE payload). This implementation transmits
   // only one PATH_CHALLENGE per connectivity probe, so only one
   // QuicPathFrameBuffer is needed.