Rename arena_destroy() to arena_reset()

This function might free memory and whatnot, but it leaves the arena
object in a usable state, so the "reset" terminology is more
appropriate.

src/lib/lwan-arena.c

@@ -28,7 +28,7 @@ void arena_init(struct arena *a)
     a->bump_ptr_alloc.remaining = 0;
 }
 
-void arena_destroy(struct arena *a)
+void arena_reset(struct arena *a)
 {
     void **iter;
 
@@ -77,10 +77,10 @@ void *arena_alloc(struct arena *a, size_t sz)
     return arena_bump_ptr(a, sz);
 }
 
-static void destroy_arena(void *data)
+static void reset_arena(void *data)
 {
     struct arena *arena = data;
-    arena_destroy(arena);
+    arena_reset(arena);
 }
 
 struct arena *coro_arena_new(struct coro *coro)
@@ -89,7 +89,7 @@ struct arena *coro_arena_new(struct coro *coro)
 
     if (LIKELY(arena)) {
         arena_init(arena);
-        coro_defer(coro, destroy_arena, arena);
+        coro_defer(coro, reset_arena, arena);
     }
 
     return arena;

src/lib/lwan-arena.h

@@ -36,6 +36,6 @@ struct arena {
 
 void arena_init(struct arena *a);
 struct arena *coro_arena_new(struct coro *coro);
-void arena_destroy(struct arena *a);
+void arena_reset(struct arena *a);
 
 void *arena_alloc(struct arena *a, size_t sz);

src/lib/lwan-mod-fastcgi.c

@@ -616,7 +616,7 @@ static bool build_stdin_records(struct lwan_request *request,
                     return false;
                 }
                 iovec_array_reset(iovec_array);
-                arena_destroy(arena);
+                arena_reset(arena);
             }
 
             to_send -= block_size;