static-delta: increase threshold for rollsum to 50%

It favours bsdiff usage for files that are not very rollsum friendly.

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

src/libostree/ostree-repo-static-delta-compilation.c

@@ -568,10 +568,10 @@ try_content_rollsum (OstreeRepo                       *repo,
 
   { guint match_ratio = (matches->bufmatches*100)/matches->total;
 
-    /* Only proceed if the file contains (arbitrary) more than 25% of
+    /* Only proceed if the file contains (arbitrary) more than 50% of
      * the previous chunks.
      */
-    if (match_ratio < 25)
+    if (match_ratio < 50)
       {
         ret = TRUE;
         goto out;