CHROMIUMOS: mwifiex: Disable transmit aggregation

CHROMIUMOS: mwifiex: Disable transmit aggregation

Disable requesting transmit aggregation.  In situations where
the firmware receives a particular type of ADDBA response, it
enters a Block-Ack-Request loop and no further frames are
transmitted.  Until this larger issue is addressed, we cannot
safely request aggregation.

Signed-off-by: Paul Stewart <pstew@chromium.org>
BUG=chrome-os-partner:12192
TEST=Associate with modified mac80211-based AP which returns
a Block-Ack-ADDBA response with only 1 buffer allowed.

Change-Id: Icb532a118bb90eca867784fd9b05bf850404e974
Reviewed-on: https://gerrit.chromium.org/gerrit/38483
Reviewed-by: Christopher Wiley <wiley@chromium.org>
Reviewed-by: mukesh agrawal <quiche@chromium.org>
Commit-Ready: Paul Stewart <pstew@chromium.org>
Tested-by: Paul Stewart <pstew@chromium.org>