iperf3: fix build-deps qa warning

Add PACKAGECONFIG lksctp to fix qa warning:

| WARNING: QA Issue: iperf3 rdepends on lksctp-tools, but it isn't a
| build dependency? [build-deps]

Signed-off-by: Kai Kang <kai.kang@windriver.com>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>