doc: netlink: Add hyperlinks to generated Netlink docs

Update ynl-gen-rst to generate hyperlinks to definitions, attribute
sets and sub-messages from all the places that reference them.

Note that there is a single label namespace for all of the kernel docs.
Hyperlinks within a single netlink doc need to be qualified by the
family name to avoid collisions.

The label format is 'family-type-name' which gives, for example,
'rt-link-attribute-set-link-attrs' as the link id.

Signed-off-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://lore.kernel.org/r/20240329135021.52534-3-donald.hunter@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>