mac80211: Allow nonHT/HT peering in mesh

Now that we have protection enabled, allow non-HT and HT20 stations to peer
with HT40+/- stations. Peering is still disallowed for HT40+/- mismatch.

Signed-off-by: Ashok Nagarajan <ashok@cozybit.com>
Reviewed-by: Thomas Pedersen <thomas@cozybit.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>