autotest (wifi): test malformed probe responses

Add autotest for malformed probe response packets.  This test covers
probe responses that include an element with an incorrect tag length.

This test covers a case where a malformed probe response may have been
the cause of a lucas device wifi disconnect.  The probe response had
an incorrect length field.  This test reproduces the scenario by
triggering a valid probe request.  The AP in the test is configured to
repeatedly send out unsolicited (malformed) probe responses.  To reduce
test flake, multiple attempts are made to receive a probe response.
The test fails if no probe responses are received, the device
disconnects or if the wifi card resets.

BUG=chromium:498018
TEST=tested on pit and lucas in wifi dev cell

Change-Id: Ib1902ab21503c65ce5028b3395ddf6f37de6888c
Reviewed-on: https://chromium-review.googlesource.com/278251
Reviewed-by: mukesh agrawal <quiche@chromium.org>
Tested-by: Rebecca Silberstein <silberst@chromium.org>
Commit-Queue: Rebecca Silberstein <silberst@chromium.org>
5 files changed