net80211: correct check for SMPS node flags updates

Update node flags when driver supports SMPS, not when it is disabled or
in dynamic mode ((iv_htcaps & HTCAP_SMPS) != 0).

Checked with RTL8188EE (1T1R), STA mode - 'smps' word should disappear
from 'ifconfig wlan0' output.

MFC after: 2 weeks