protocol: add security label to a client

Don't pass the ucred to the client construct, just set the properties
in the protocol.
Use the client properties to get ucred.
Add the security label to the client properties (from SO_PEERSEC)

src/modules/module-protocol-native/test-connection.c

@@ -22,6 +22,8 @@
  * DEALINGS IN THE SOFTWARE.
  */
 
+#include <sys/socket.h>
+
 #include <spa/pod/parser.h>
 
 #include <pipewire/pipewire.h>