mac80211: fix rx flow sparse errors, make functions static

This patch adds static declarations to functions in the Rx flow in order to
eliminate sparse errors

Signed-off-by: Ron Rindjunsky <ron.rindjunsky@intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>