staging: wlan-ng: rename DIDmsg_lnxreq_wlansniff in p80211metadef.h

Rename DIDmsg_lnxreq_wlansniff in p80211metadef.h to
DIDMSG_LNXREQ_WLANSNIFF to fix "Avoid CamelCase" message from
checkpatch and conform to the coding style guidelines.

Signed-off-by: Tim Collier <osdevtc@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>