mac80211: initialize SMPS field in HT capabilities

ibss and mesh modes copy the ht capabilites from the band without
overriding the SMPS state. Unfortunately the default value 0 for the
SMPS field means static SMPS instead of disabled.

This results in HT ibss and mesh setups using only single-stream rates,
even though SMPS is not supposed to be active.

Initialize SMPS to disabled for all bands on ieee80211_hw_register to
ensure that the value is sane where it is not overriden with the real
SMPS state.

Reported-by: Elektra Wagenrad <onelektra@gmx.net>
Signed-off-by: Felix Fietkau <nbd@nbd.name>
[move VHT TODO comment to a better place]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>