staging: wlan-ng: Fix restricted __be16 degrades to integer

skb->protocol variable type is __be16 and in if condition
it is comparing with ETH_P_80211_RAW constant variable
which is not __be16 type. Using be16_to_cpu() function,
value of skb->protocol converted native processor format.
This bug was found by sparse.

Signed-off-by: Ebru Akagunduz <ebru.akagunduz@gmail.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>