Rework SsdpHttpClient

MediaBrowser.Common/Net/NamedClient.cs

@@ -14,5 +14,10 @@
         /// Gets the value for the MusicBrainz named http client.
         /// </summary>
         public const string MusicBrainz = nameof(MusicBrainz);
+
+        /// <summary>
+        /// Gets the value for the DLNA named http client.
+        /// </summary>
+        public const string Dlna = nameof(Dlna);
     }
 }