Net80211s update: Mesh Gate Announcement and removal of Portal Announcement.

Net80211s update: Mesh Gate Announcement and removal of Portal Announcement.

 * Renamed IEEE80211_ELEMID_MESHPANN to IEEE80211_ELEMID_MESHGANN according to
 amendment;
 * Added IEEE80211_IOC_MESH_GATE that controls whether Mesh Gate Announcement
 is activated or not;
 * Renamed all flags from Portal to Gate in HWMP frames;
 * Removed IEEE80211_ACTION_MESHPANN enum cause its part of the Mesh Action
 category now as per amendment;
 * Renamed IEEE80211_MESHFLAGS_PORTAL to IEEE80211_MESHFLAGS_GATE in
 ieee80211_mesh_state flags;
 * Modified ieee80211_hwmp.c/ieee80211_mesh.c to use new GATE flags;

Approved by: adrian