wl1251: make local symbols static

Make local functions and data static, also constify
some structures. While at it, clean up unneeded includes.

Signed-off-by: Grazvydas Ignotas <notasas@gmail.com>
Cc: Bob Copeland <me@bobcopeland.com>
Acked-by: Kalle Valo <kalle.valo@iki.fi>
Signed-off-by: John W. Linville <linville@tuxdriver.com>