nl80211: Replace interface socket owner attribute with more generic one

Replace NL80211_ATTR_IFACE_SOCKET_OWNER attribute with more generic
NL80211_ATTR_SOCKET_OWNER that can be used with other commands
that interface creation.

Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>