Bluetooth-OBEX: Fine tune OBEX Tx MTU for better performace/power

This will change improve Tx throughput and better power numbers
during operation.

CRs-Fixed: 625250
Change-Id: Ife61b1e48c633c3ea2f7bba7afce21c7c16ddd85

Conflicts:
	obex/javax/obex/ObexHelper.java