Label random-noise sources with an enum of ids.

The upcoming PRNG revamp will want to tell noise sources apart, so
that it can treat them all fairly. So I've added an extra parameter to
noise_ultralight and random_add_noise, which takes values in an
enumeration covering all the vague classes of entropy source I'm
collecting. In this commit, though, it's simply ignored.

unix/uxplink.c

@@ -958,7 +958,7 @@ int main(int argc, char **argv)
 
             if (backend_connected(backend)) {
 		ret = read(STDIN_FILENO, buf, sizeof(buf));
-                noise_ultralight(ret);
+                noise_ultralight(NOISE_SOURCE_IOLEN, ret);
 		if (ret < 0) {
 		    perror("stdin: read");
 		    exit(1);