mwifiex: remove redundant TDLS setup action frame check and avoid leaks

The unwanted frame types are already handled in 'default' case
of the switch/case below.
The str_ptr is allocated but it can be leaked if the length check
fails in the REQUEST/RESP cases. Fix it by allocating sta_ptr
after the length checks.

Reported-by: Paul Stewart <pstew@chromium.org>
Signed-off-by: Bing Zhao <bzhao@marvell.com>
Signed-off-by: Avinash Patil <patila@marvell.com>
Signed-off-by: Paul Stewart <pstew@chromium.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>