Staging: wlan-ng: Improved case statements in p80211req_mibset_mibget()

This patch improves code from p80211req_mibset_mibget() function by
taking into account that every
DIDmib_dot11smt_dot11WEPDefaultKeysTable_dot11WEPDefaultKeyX with
X in {0, 1, 2, 3} is a bit mask where the (P80211DID_MASK_ITEM <<
P80211DID_LSB_ITEM) mask aka 0x0x0003f000 mask keeps bits representing
the DID item number. To get this item number use P80211DID_ITEM().

Signed-off-by: Claudiu Beznea <claudiu.beznea@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>