Implemented memory clean up for digest cache list

Upon fwknopd shutdown, a new function free_replay_list() is now called in order
to free heap allocated memory dedicated to SPA digest tracking.  Without this
fix, valgrind reports the following (some output snipped):

valgrind --leak-check=full ./server/.libs/fwknopd -f -i lo -P "udp port 62201"

==30864== 431 (48 direct, 383 indirect) bytes in 1 blocks are definitely lost in loss record 17 of 17
==30864==    at 0x4C27480: calloc (vg_replace_malloc.c:467)
==30864==    by 0x407CB7: replay_check_file_cache (replay_cache.c:461)
==30864==    by 0x407B69: replay_check (replay_cache.c:413)
==30864==    by 0x405813: incoming_spa (incoming_spa.c:363)
==30864==    by 0x406275: pcap_capture (pcap_capture.c:223)
==30864==    by 0x40317D: main (fwknopd.c:297)

server/fwknopd.c

@@ -366,6 +366,11 @@ main(int argc, char **argv)
     */
     fw_cleanup();
     free_logging();
+
+#if USE_FILE_CACHE
+    free_replay_list(&opts);
+#endif
+
     free_configs(&opts);
 
     return(0);

server/replay_cache.c

@@ -619,4 +619,36 @@ replay_check_dbm_cache(fko_srv_options_t *opts, fko_ctx_t ctx)
 }
 #endif /* USE_FILE_CACHE */
 
+#if USE_FILE_CACHE
+/* Free replay list memory
+*/
+void
+free_replay_list(fko_srv_options_t *opts)
+{
+#ifdef NO_DIGEST_CACHE
+    return;
+#endif
+    struct digest_cache_list *digest_list_ptr = NULL, *digest_tmp = NULL;
+
+    if (opts->digest_cache == NULL)
+        return;
+
+    digest_list_ptr = opts->digest_cache;
+    while (digest_list_ptr != NULL)
+    {
+        digest_tmp = digest_list_ptr->next;
+        if (digest_list_ptr->cache_info.digest != NULL
+                && digest_list_ptr->cache_info.digest[0] != '\0')
+        {
+            free(digest_list_ptr->cache_info.digest);
+        }
+        free(digest_list_ptr);
+        digest_list_ptr = digest_tmp;
+    }
+
+    return;
+}
+#endif
+
+
 /***EOF***/

server/replay_cache.h

@@ -63,6 +63,7 @@ int replay_check(fko_srv_options_t *opts, fko_ctx_t ctx);
 #ifdef USE_FILE_CACHE
 int replay_file_cache_init(fko_srv_options_t *opts);
 int replay_check_file_cache(fko_srv_options_t *opts, fko_ctx_t ctx);
+void free_replay_list(fko_srv_options_t *opts);
 #else
 int replay_db_cache_init(fko_srv_options_t *opts);
 int replay_check_dbm_cache(fko_srv_options_t *opts, fko_ctx_t ctx);