cfg80211: add MPLS and 802.21 classification

MPLS labels may contain traffic control information, which should be
evaluated and used by the wireless subsystem if present.

Also check for IEEE 802.21 which is always network control traffic.

Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
Signed-off-by: Mathias Kretschmer <mathias.kretschmer@fokus.fraunhofer.de>
Acked-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: David S. Miller <davem@davemloft.net>