MULE-7664 Allow size of internal buffer used for copy streams to be cust...

...omized
Agree that the change is not flexible enough, but its more flexible than before and I think the change is small enough to be part of a minor release.
On the other side, given that there are not enough information that this will cause a performance improvement, my vote is to leave this change out of 3.5.x and work on the changes MG suggested for 3.6.x