mwifiex: fix Tx data rate display issue

"iw dev mlan0 link" shows wrong data rate, because data rate is
not sent properly to cfg80211 stack. Also stack is not updated
with mcs and Tx data flags information.

Signed-off-by: Amitkumar Karwar <akarwar@marvell.com>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>