Fix error message with invalid Geneve option length.
diff --git a/print-geneve.c b/print-geneve.c
index 7550ba0..55a076e 100644
--- a/print-geneve.c
+++ b/print-geneve.c
@@ -183,7 +183,7 @@
 
     if (len < opts_len) {
         ND_PRINT((ndo, " truncated-geneve - %u bytes missing",
-                  len - opts_len));
+                  opts_len - len));
         return;
     }