Using setting for unix socket response buffer size

On networks with about 200 upnp devices, search type 3 (all) truncates the full response.  Adding a configuration setting that allows for building minissdpd to have a larger buffer for the response.

minissdpd/minissdpd.c

@@ -726,7 +726,7 @@ void processRequest(struct reqelem * req)
 	const unsigned char * p;
 	int type;
 	struct device * d = devlist;
-	unsigned char rbuf[4096];
+	unsigned char rbuf[RESPONSE_BUFFER_SIZE];
 	unsigned char * rp = rbuf+1;
 	unsigned char nrep = 0;
 	time_t t;