libertas: rename and clean up DownloadcommandToStation

Call it lbs_submit_command(), remove a bunch of things which can be (or,
in the case of zeroing ->cmdwaitqwoken, already are) done elsewhere.

Signed-off-by: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>