doc: Bump DOT_GRAPH_MAX_NODES from 50 to 100

This avoids doxygen truncating the graphs due to too many nodes, and
the accompanying warnings.

doc/Doxyfile.in

@@ -2306,7 +2306,7 @@ PLANTUML_JAR_PATH      =
 # Minimum value: 0, maximum value: 10000, default value: 50.
 # This tag requires that the tag HAVE_DOT is set to YES.
 
-DOT_GRAPH_MAX_NODES    = 50
+DOT_GRAPH_MAX_NODES    = 100
 
 # The MAX_DOT_GRAPH_DEPTH tag can be used to set the maximum depth of the graphs
 # generated by dot. A depth value of 3 means that only nodes reachable from the