vppinfra: finish deprecating qsort.c

Minor change to vec_sort_with_function(...): don't depend on the qsort
implementation to deal with null, zero-long, or 1-long vectors

Type: fix

Signed-off-by: Dave Barach <dave@barachs.net>
Change-Id: I7bd7b0421673d2a025363089562aa7c6266fba66
(cherry picked from commit f593b5792031b3797cdcdfd3fbb33ac4de8c9a5d)

src/vppinfra/vec.h

@@ -974,11 +974,15 @@ do {						\
 
 /** \brief Sort a vector using the supplied element comparison function
 
+    Does not depend on the underlying implementation to deal correctly
+    with null, zero-long, or 1-long vectors
+
     @param vec vector to sort
     @param f comparison function
 */
 #define vec_sort_with_function(vec,f)                           \
 do {                                                            \
+  if (vec_len (vec) > 1)                                        \
     qsort (vec, vec_len (vec), sizeof (vec[0]), (void *) (f));  \
 } while (0)