net: airoha: Avoid -Wflex-array-member-not-at-end warning

-Wflex-array-member-not-at-end was introduced in GCC-14, and we are
getting ready to enable it, globally.

Move the conflicting declaration to the end of the corresponding
structure. Notice that `struct airoha_foe_entry` is a flexible
structure, this is a structure that contains a flexible-array
member.

Fix the following warning:

drivers/net/ethernet/airoha/airoha_eth.h:474:33: warning: structure containing a flexible array member is not at the end of another structure [-Wflex-array-member-not-at-end]

Signed-off-by: Gustavo A. R. Silva <[e-mail]>
Reviewed-by: Simon Horman <[e-mail]>
Link: https://patch.msgid.link/aNFYVYLXQDqm4yxb@kspp
Signed-off-by: Jakub Kicinski <[e-mail]>

drivers/net/ethernet/airoha/airoha_eth.h

···
 		};
 	};
 
-	struct airoha_foe_entry data;
 	struct hlist_node l2_subflow_node; /* PPE L2 subflow entry */
 	u32 hash;
 
···
 
 	struct rhash_head node;
 	unsigned long cookie;
+
+	/* Must be last --ends in a flexible-array member. */
+	struct airoha_foe_entry data;
 };
 
 struct airoha_wdma_info {