The tc spec referenced tc-u32-mark and tc-act-police-attrs but did not
define them. The missing definitions were discovered when building the
docs with generated hyperlinks because the hyperlink target labels were
missing.

Add definitions for tc-u32-mark and tc-act-police-attrs.
Signed-off-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://lore.kernel.org/r/20240329135021.52534-4-donald.hunter@gmail.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>