mwifiex: initialize Tx/Rx info of a packet correctly

There are few places at the begining of Tx/Rx paths where
tx_info/rx_info is not correctly initialized. This patch
takes care of it.

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