net: netlink: recommend policy range validation

For large ranges (outside of s16) the documentation currently
recommends open-coding the validation, but it's better to use
the NLA_POLICY_FULL_RANGE() or NLA_POLICY_FULL_RANGE_SIGNED()
policy validation instead; recommend that.

Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://lore.kernel.org/r/20230127084506.09f280619d64.I5dece85f06efa8ab0f474ca77df9e26d3553d4ab@changeid
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: jmberg-intel

include/net/netlink.h

@@ -276,7 +276,8 @@ enum nla_policy_validation {
  *                         Note that in the interest of code simplicity and
  *                         struct size both limits are s16, so you cannot
  *                         enforce a range that doesn't fall within the range
- *                         of s16 - do that as usual in the code instead.
+ *                         of s16 - do that using the NLA_POLICY_FULL_RANGE()
+ *                         or NLA_POLICY_FULL_RANGE_SIGNED() macros instead.
  *                         Use the NLA_POLICY_MIN(), NLA_POLICY_MAX() and
  *                         NLA_POLICY_RANGE() macros.
  *    NLA_U8,