wireless: use OR operation to set wiphy features

The next patch will introduce a flag that is set
by default in cfg80211 so drivers and mac80211
need to use |= to set features they have so that
they don't clear the already-set feature.

We could set the flag in wiphy_register() instead
of wiphy_new() to avoid this patch, but then the
drivers couldn't *unset* flags they don't want to
use even though the implementation is generic.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>