doc: Document the type of label EVP_PKEY_CTX_set0_rsa_oaep_label properly

Reviewed-by: NMatt Caswell <matt@openssl.org>
Reviewed-by: NShane Lontis <shane.lontis@oracle.com>
(Merged from https://github.com/openssl/openssl/pull/16869)

doc/man3/EVP_PKEY_CTX_ctrl.pod

@@ -116,7 +116,7 @@ EVP_PKEY_CTX_set_kem_op
  int EVP_PKEY_CTX_get_rsa_oaep_md(EVP_PKEY_CTX *ctx, const EVP_MD **md);
  int EVP_PKEY_CTX_get_rsa_oaep_md_name(EVP_PKEY_CTX *ctx, char *name,
                                        size_t namelen);
- int EVP_PKEY_CTX_set0_rsa_oaep_label(EVP_PKEY_CTX *ctx, unsigned char *label,
+ int EVP_PKEY_CTX_set0_rsa_oaep_label(EVP_PKEY_CTX *ctx, void *label,
                                       int len);
  int EVP_PKEY_CTX_get0_rsa_oaep_label(EVP_PKEY_CTX *ctx, unsigned char **label);
 
@@ -356,8 +356,8 @@ EVP_MD object instead. Note that only known, built-in EVP_MD objects will be
 returned. The EVP_MD object may be NULL if the digest is not one of these (such
 as a digest only implemented in a third party provider).
 
-EVP_PKEY_CTX_set0_rsa_oaep_label() sets the RSA OAEP label to
-I<label> and its length to I<len>. If I<label> is NULL or I<len> is 0,
+EVP_PKEY_CTX_set0_rsa_oaep_label() sets the RSA OAEP label to binary data
+I<label> and its length in bytes to I<len>. If I<label> is NULL or I<len> is 0,
 the label is cleared. The library takes ownership of the label so the
 caller should not free the original memory pointed to by I<label>.
 The padding mode must have been set to B<RSA_PKCS1_OAEP_PADDING>.