Fix a gfe_quic_fuzzer issue caused by uninitialized packet number.

gfe-relnote: (n/a) Test only.
PiperOrigin-RevId: 278637204
Change-Id: Ica4277aa9962c206cd7f1d7acbb3a713f88309eb

quic/core/quic_packet_number.h

diff --git a/quic/core/quic_packet_number.h b/quic/core/quic_packet_number.h
index 8a75149..18e78bb 100644
--- a/quic/core/quic_packet_number.h
+++ b/quic/core/quic_packet_number.h
@@ -31,6 +31,11 @@
         << "Use default constructor for uninitialized packet number";
   }
 
+  // The sentinel value representing an uninitialized packet number.
+  static constexpr uint64_t UninitializedPacketNumber() {
+    return std::numeric_limits<uint64_t>::max();
+  }
+
   // Packet number becomes uninitialized after calling this function.
   void Clear();
 
@@ -84,11 +89,6 @@
   // REQUIRES: lhs >= rhs.
   friend inline uint64_t operator-(QuicPacketNumber lhs, QuicPacketNumber rhs);
 
-  // The sentinel value representing an uninitialized packet number.
-  static constexpr uint64_t UninitializedPacketNumber() {
-    return std::numeric_limits<uint64_t>::max();
-  }
-
   uint64_t packet_number_;
 };