nl80211: Fix mesh HT operation check

A previous change to fix checks for NL80211_MESHCONF_HT_OPMODE
missed setting the flag when replacing FILL_IN_MESH_PARAM_IF_SET
with checking codes. This results in dropping the received HT
operation value when called by nl80211_update_mesh_config(). Fix
this by setting the flag properly.

Fixes: 9757235f ("nl80211: correct checks for NL80211_MESHCONF_HT_OPMODE value")
Signed-off-by: Masashi Honma <masashi.honma@gmail.com>
[rewrite commit message to use Fixes: line]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>