mac80211: don't set mesh peer ht caps if ht disabled

Blindly setting ht caps on a mesh peer's station entry would result in
MCS rates being used by the rate control algorithm even if no ht had
been configured. Fix this by checking the channel type before assigning
ht capabilites.

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