netlink: specs: rename rtnetlink specs in accordance with family name

netlink: specs: rename rtnetlink specs in accordance with family name

The rtnetlink family names are set to rt-$name within the YAML
but the files are called rt_$name. C codegen assumes that the
generated file name will match the family. The use of dashes
is in line with our general expectation that name properties
in the spec use dashes not underscores (even tho, as Donald
points out most genl families use underscores in the name).

We have 3 un-ideal options to choose from:

 - accept the slight inconsistency with old families using _, or
 - accept the slight annoyance with all languages having to do s/-/_/
   when looking up family ID, or
 - accept the inconsistency with all name properties in new YAML spec
   being separated with - and just the family name always using _.

Pick option 1 and rename the rtnl spec files.

Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://patch.msgid.link/20250410014658.782120-2-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>