MINOR: pools: make sure 'no-memory-trimming' is always used

The global option 'no-memory-trimming' was added in 2.6 with commit
c4e56dc58 ("MINOR: pools: add a new global option "no-memory-trimming"")
but there were some cases left where it was not considered. Let's make
is_trim_enabled() also consider it.
diff --git a/src/pool.c b/src/pool.c
index 214d950..908b334 100644
--- a/src/pool.c
+++ b/src/pool.c
@@ -213,7 +213,7 @@
 
 int is_trim_enabled(void)
 {
-	return using_default_allocator;
+	return !disable_trim && using_default_allocator;
 }
 
 static int mem_should_fail(const struct pool_head *pool)