netfilter: nf_tables: constify struct nft_ctx * parameter in nft_trans_alloc()

Context is not modified by nft_trans_alloc(), so constify it.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_tables_api.c

@@ -111,8 +111,8 @@ static void nft_ctx_init(struct nft_ctx *ctx,
 	ctx->seq	= nlh->nlmsg_seq;
 }
 
-static struct nft_trans *nft_trans_alloc(struct nft_ctx *ctx, int msg_type,
-					 u32 size)
+static struct nft_trans *nft_trans_alloc(const struct nft_ctx *ctx,
+					 int msg_type, u32 size)
 {
 	struct nft_trans *trans;