nl80211: Allow set network namespace by fd

Added new NL80211_ATTR_NETNS_FD which allows to
set namespace via nl80211 by fd.

Signed-off-by: Vadim Kochan <vadim4j@gmail.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/core/net_namespace.c

@@ -361,6 +361,7 @@ struct net *get_net_ns_by_fd(int fd)
 	return ERR_PTR(-EINVAL);
 }
 #endif
+EXPORT_SYMBOL_GPL(get_net_ns_by_fd);
 
 struct net *get_net_ns_by_pid(pid_t pid)
 {