TUN-9882: Bump datagram v3 write channel capacity

Bumping from 16 to 512 gives each flow a bit more buffer if the local OS is having trouble writing to the origin.

Closes TUN-9882

Author: DevinCarr

quic/v3/session.go

@@ -26,7 +26,7 @@ const (
 	// The maximum amount of datagrams a session will queue up before it begins dropping datagrams.
 	// This channel buffer is small because we assume that the dedicated writer to the origin is typically
 	// fast enought to keep the channel empty.
-	writeChanCapacity = 16
+	writeChanCapacity = 512
 
 	logFlowID        = "flowID"
 	logPacketSizeKey = "packetSize"