netlink: hide validation union fields from kdoc

Mark the validation fields as private, users shouldn't set
them directly and they are too complicated to explain in
a more succinct way (there's already a long explanation
in the comment above).

The strict_start_type field is set directly and has a dedicated
comment so move that above the "private" section.

Link: https://lore.kernel.org/r/20221027212107.2639255-1-kuba@kernel.orgSigned-off-by: NJakub Kicinski <kuba@kernel.org>

include/net/netlink.h

@@ -317,19 +317,10 @@ struct nla_policy {
 	u8		validation_type;
 	u16		len;
 	union {
-		const u32 bitfield32_valid;
-		const u32 mask;
-		const char *reject_message;
-		const struct nla_policy *nested_policy;
-		struct netlink_range_validation *range;
-		struct netlink_range_validation_signed *range_signed;
-		struct {
-			s16 min, max;
-			u8 network_byte_order:1;
-		};
-		int (*validate)(const struct nlattr *attr,
-				struct netlink_ext_ack *extack);
-		/* This entry is special, and used for the attribute at index 0
+		/**
+		 * @strict_start_type: first attribute to validate strictly
+		 *
+		 * This entry is special, and used for the attribute at index 0
 		 * only, and specifies special data about the policy, namely it
 		 * specifies the "boundary type" where strict length validation
 		 * starts for any attribute types >= this value, also, strict
@@ -348,6 +339,20 @@ struct nla_policy {
 		 * was added to enforce strict validation from thereon.
 		 */
 		u16 strict_start_type;
+
+		/* private: use NLA_POLICY_*() to set */
+		const u32 bitfield32_valid;
+		const u32 mask;
+		const char *reject_message;
+		const struct nla_policy *nested_policy;
+		struct netlink_range_validation *range;
+		struct netlink_range_validation_signed *range_signed;
+		struct {
+			s16 min, max;
+			u8 network_byte_order:1;
+		};
+		int (*validate)(const struct nlattr *attr,
+				struct netlink_ext_ack *extack);
 	};
 };