(split) Rename definition of IEEE80211_FC1_WEP to IEEE80211_FC1_PROTECTED.

The origin of WEP comes from IEEE Std 802.11-1997 where it defines
whether the frame body of MAC frame has been encrypted using WEP
algorithm or not.
IEEE Std. 802.11-2007 changes WEP to Protected Frame, indicates
whether the frame is protected by a cryptographic encapsulation
algorithm.

Reviewed by:	adrian, rpaulo
(split) Merge branch 'CURRENT' (commit 'c23c0c9f')