netfilter: nf_tables: statify nft_expr_init()

Not exposed anymore to modules, statify this function.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/net/netfilter/nf_tables.h

@@ -846,8 +846,6 @@ static inline void *nft_expr_priv(const struct nft_expr *expr)
 	return (void *)expr->data;
 }
 
-struct nft_expr *nft_expr_init(const struct nft_ctx *ctx,
-			       const struct nlattr *nla);
 void nft_expr_destroy(const struct nft_ctx *ctx, struct nft_expr *expr);
 int nft_expr_dump(struct sk_buff *skb, unsigned int attr,
 		  const struct nft_expr *expr);