iperf: fix "speed" display in csv report

iperf: fix "speed" display in csv report

Some parameters displayed in the CSV reports are declared
as uint64_t, but the printf format doesn't reflect this.

Submitted bug: https://sourceforge.net/p/iperf/bugs/66/

Signed-off-by: Matt Poduska <matt.poduska@rockwellcollins.com>
Signed-off-by: Atul Singh <atul.singh.mandla@rockwellcollins.com>
Signed-off-by: Matt Weber <matthew.weber@rockwellcollins.com>
Reviewed-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>