crypto: user - fix potential warnings in cryptouser.h

Function definitions in headers are usually marked as 'static inline'.

Since 'inline' is missing for crypto_reportstat(), if it were not
referenced from a .c file that includes this header, it would produce
a warning.

Also, 'struct crypto_user_alg' is not declared in this header.

I included <linux/crytouser.h> instead of adding the forward declaration
as suggested [1].

Detected by compile-testing this header as a standalone unit:

./include/crypto/internal/cryptouser.h:6:44: warning: ‘struct crypto_user_alg’ declared inside parameter list will not be visible outside of this definition or declaration
 struct crypto_alg *crypto_alg_match(struct crypto_user_alg *p, int exact);
                                            ^~~~~~~~~~~~~~~
./include/crypto/internal/cryptouser.h:11:12: warning: ‘crypto_reportstat’ defined but not used [-Wunused-function]
 static int crypto_reportstat(struct sk_buff *in_skb, struct nlmsghdr *in_nlh, struct nlattr **attrs)
            ^~~~~~~~~~~~~~~~~

[1] https://lkml.org/lkml/2019/6/13/1121Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

include/crypto/internal/cryptouser.h

 /* SPDX-License-Identifier: GPL-2.0 */
+#include <linux/cryptouser.h>
 #include <net/netlink.h>
 
 struct crypto_alg *crypto_alg_match(struct crypto_user_alg *p, int exact);
@@ -6,7 +7,9 @@ struct crypto_alg *crypto_alg_match(struct crypto_user_alg *p, int exact);
 #ifdef CONFIG_CRYPTO_STATS
 int crypto_reportstat(struct sk_buff *in_skb, struct nlmsghdr *in_nlh, struct nlattr **attrs);
 #else
-static int crypto_reportstat(struct sk_buff *in_skb, struct nlmsghdr *in_nlh, struct nlattr **attrs)
+static inline int crypto_reportstat(struct sk_buff *in_skb,
+				    struct nlmsghdr *in_nlh,
+				    struct nlattr **attrs)
 {
 	return -ENOTSUPP;
 }