nfp: Annotate struct nfp_reprs with __counted_by

Prepare for the coming implementation by GCC and Clang of the __counted_by
attribute. Flexible array members annotated with __counted_by can have
their accesses bounds-checked at run-time via CONFIG_UBSAN_BOUNDS (for
array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
functions).

As found with Coccinelle[1], add __counted_by for struct nfp_reprs.

Cc: Simon Horman <simon.horman@corigine.com>
Cc: oss-drivers@corigine.com
Link: https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci [1]
Signed-off-by: Kees Cook <keescook@chromium.org>
Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Acked-by: Louis Peens <louis.peens@corigine.com>
Link: https://lore.kernel.org/r/20231003231843.work.811-kees@kernel.orgSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/netronome/nfp/nfp_net_repr.h

@@ -18,7 +18,7 @@ struct nfp_port;
  */
 struct nfp_reprs {
 	unsigned int num_reprs;
-	struct net_device __rcu *reprs[];
+	struct net_device __rcu *reprs[] __counted_by(num_reprs);
 };
 
 /**