Allow the transport to specify the maximum segment length.

api/net/sf/briar/api/plugins/SegmentSink.java

@@ -8,4 +8,9 @@ public interface SegmentSink {
 
 	/** Writes the given segment. */
 	void writeSegment(Segment s) throws IOException;
+
+	/**
+	 * Returns the maximum length in bytes of the segments this sink accepts.
+	 */
+	int getMaxSegmentLength();
 }

api/net/sf/briar/api/plugins/SegmentSource.java

@@ -11,4 +11,9 @@ public interface SegmentSource {
 	 * segment was read, or false if no more segments can be read.
 	 */
 	boolean readSegment(Segment s) throws IOException;
+
+	/**
+	 * Returns the maximum length in bytes of the segments this source returns.
+	 */
+	int getMaxSegmentLength();
 }