conn: inch BatchSize toward being non-dynamic

There's not really a use at the moment for making this configurable, and
once bind_windows.go behaves like bind_std.go, we'll be able to use
constants everywhere. So begin that simplification now.

Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

conn/conn.go

@@ -16,7 +16,7 @@ import (
 )
 
 const (
-	DefaultBatchSize = 128 // maximum number of packets handled per read and write
+	IdealBatchSize = 128 // maximum number of packets handled per read and write
 )
 
 // A ReceiveFunc receives at least one packet from the network and writes them