[WifiStressTest.py] Fix iperf server stop issue

Stopping iperf server is called before cleaning up AP. Exception is
thrown when this process is not killed and AP cleanup never happens.
Moving this below the AP cleanup

Bug: 134771317
Test: None
Change-Id: I52782ae1a2ba8601840950ff3eabc5e0d9bec1ed
1 file changed
tree: 5e08ac89ce6d0ba949af326b19f100d82429735a
  1. acts/
  2. tools/
  3. wts-acts/
  4. Android.mk
  5. OWNERS
  6. PREUPLOAD.cfg