avfilter/paletteuse: switch to recursive method

It appears faster than the iterative method on my machine (1.06x
faster), so I'm guessing compilers improved over time (the iterative
version was slightly faster in the past).

libavfilter/vf_paletteuse.c

@@ -130,7 +130,7 @@ static const AVOption paletteuse_options[] = {
 
     /* following are the debug options, not part of the official API */
     { "debug_kdtree", "save Graphviz graph of the kdtree in specified file", OFFSET(dot_filename), AV_OPT_TYPE_STRING, {.str=NULL}, 0, 0, FLAGS },
-    { "color_search", "set reverse colormap color search method", OFFSET(color_search_method), AV_OPT_TYPE_INT, {.i64=COLOR_SEARCH_NNS_ITERATIVE}, 0, NB_COLOR_SEARCHES-1, FLAGS, "search" },
+    { "color_search", "set reverse colormap color search method", OFFSET(color_search_method), AV_OPT_TYPE_INT, {.i64=COLOR_SEARCH_NNS_RECURSIVE}, 0, NB_COLOR_SEARCHES-1, FLAGS, "search" },
         { "nns_iterative", "iterative search",             0, AV_OPT_TYPE_CONST, {.i64=COLOR_SEARCH_NNS_ITERATIVE}, INT_MIN, INT_MAX, FLAGS, "search" },
         { "nns_recursive", "recursive search",             0, AV_OPT_TYPE_CONST, {.i64=COLOR_SEARCH_NNS_RECURSIVE}, INT_MIN, INT_MAX, FLAGS, "search" },
         { "bruteforce",    "brute-force into the palette", 0, AV_OPT_TYPE_CONST, {.i64=COLOR_SEARCH_BRUTEFORCE},    INT_MIN, INT_MAX, FLAGS, "search" },