The AR req handler should not check the generation; higher level code
is the better place to handle bus generation changes.  The target node
ID just needs to be checked for not being the "all nodes" address; in
this case don't handle the request and don't respond.

Use Address_Error and Type_Error rcodes as appropriate.
Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>