staging: wlan-ng: rename DIDmib_p2_p2MAC in p80211metadef.h

Rename DIDmib_p2_p2MAC in p80211metadef.h to DIDMIB_P2_MAC to fix
"Avoid CamelCase" message from checkpatch and conform to the coding
style guidelines. Also shorten name by removing repeated use of "P2"
to ease readability and reduce long lines.

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