crypto: user - forward declare crypto_nlsk

Move the declaration of crypto_nlsk into internal/cryptouser.h.  This
fixes the following sparse warning:

    crypto/crypto_user_base.c:41:13: warning: symbol 'crypto_nlsk' was not declared. Should it be static?

Cc: Corentin Labbe <clabbe@baylibre.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/crypto_user_stat.c

@@ -22,8 +22,6 @@
 
 static DEFINE_MUTEX(crypto_cfg_mutex);
 
-extern struct sock *crypto_nlsk;
-
 struct crypto_dump_info {
 	struct sk_buff *in_skb;
 	struct sk_buff *out_skb;