flow: Fix clang error (clang-analyzer-security.PointerSub)HEADmaster

Fixes the following clang-analyzer warning:

flow_table.h:96:25: note: Subtraction of two pointers that do not point into the same array is undefined behavior
   96 |         return (union flow *)f - flowtab;

The `flow_idx()` function is called via `FLOW_IDX()` from
`flow_foreach_slot()`, where `f` is set to `&flowtab[idx].f`.
Therefore, `f` and `flowtab` do point to the same array.

Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/flow_table.h b/flow_table.h
index 2d5c65c..3f3f4b7 100644
--- a/flow_table.h
+++ b/flow_table.h
@@ -93,6 +93,7 @@ extern union flow flowtab[];
  */
 static inline unsigned flow_idx(const struct flow_common *f)
 {
+	/* NOLINTNEXTLINE(clang-analyzer-security.PointerSub) */
 	return (union flow *)f - flowtab;
 }