conn: make StdNetBind.BatchSize() return 1 for non-Linux

This commit updates StdNetBind.BatchSize() to return 1 instead of
IdealBatchSize for non-Linux platforms. Non-Linux platforms do not
yet benefit from values > 1, which only serves to increase memory
consumption.

Reviewed-by: James Tucker <james@tailscale.com>
Signed-off-by: Jordan Whited <jordan@tailscale.com>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

conn/bind_std.go

@@ -272,7 +272,10 @@ func (s *StdNetBind) makeReceiveIPv6(pc *ipv6.PacketConn, conn *net.UDPConn) Rec
 // TODO: When all Binds handle IdealBatchSize, remove this dynamic function and
 // rename the IdealBatchSize constant to BatchSize.
 func (s *StdNetBind) BatchSize() int {
-	return IdealBatchSize
+	if runtime.GOOS == "linux" {
+		return IdealBatchSize
+	}
+	return 1
 }
 
 func (s *StdNetBind) Close() error {