staging: brcm80211: replace broadcom specific auth related defines

- DOT11_OPEN_SYSTEM -> WLAN_AUTH_OPEN
- DOT11_SHARED_KEY -> WLAN_AUTH_SHARED_KEY
- remove unused DOT11_MGMT_HDR_LEN

Signed-off-by: Stanislav Fomichev <kernel@fomichev.me>
Acked-by: Roland Vossen <rvossen@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>