netlink: specs: rt_route: pull the ifa- prefix out of the names

YAML specs don't normally include the C prefix name in the name
of the YAML attr. Remove the ifa- prefix from all attributes
in route-attrs and metrics and specify name-prefix instead.

This is a bit risky, hopefully there aren't many users out there.

Fixes: 023289b4 ("doc/netlink: Add spec for rt route messages")
Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://patch.msgid.link/20250403013706.2828322-5-kuba@kernel.org


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