Revert "CHROMIUMOS: mwifiex: Disable transmit aggregation"

Revert "CHROMIUMOS: mwifiex: Disable transmit aggregation"

New firmware fixes this issue, so this change is no longer necessary.

This reverts commit 6fcfecca9575848120e8c9e35b3ad848b1e85f29

BUG=chrome-os-partner:16279
TEST=Associate with Android AP

Change-Id: Id0542875bc599bf5da23cdeb0da57739cc60c44d
Reviewed-on: https://gerrit.chromium.org/gerrit/41467
Reviewed-by: Bing Zhao <bzhao@marvell.com>
Reviewed-by: Christopher Wiley <wiley@chromium.org>
Commit-Queue: Paul Stewart <pstew@chromium.org>
Tested-by: Paul Stewart <pstew@chromium.org>