ARM: dts: msm: Specify non-default data receive mtu for MSM8916

Increasing the downlink MTU to 4k shows a 14% improvement in end-to-end
bidirectional throughput when the USB link to a host PC is bandwidth
limited.

CRs-Fixed: 678204
Change-Id: Ib565887d7efb23050a4f8ab9139a386ce148be24
Signed-off-by: Jeffrey Hugo <jhugo@codeaurora.org>