[PATCH] libertas: make more functions static & remove unused functions

Some functions where declared in header files, but used only once. They are
now static functions.

After doing this, I found out that some functions weren't used at all. I
removed this dead code.

Signed-off-by: Holger Schurig <hs4233@mail.mn-solutions.de>
Signed-off-by: John W. Linville <linville@tuxdriver.com>