src/nbd: no need to retry if we received a 404 from the server
src/nbd: no need to retry if we received a 404 from the server

If the server does not provide the requested file, this won't likely
change on subsequent tries.

Signed-off-by: Enrico Jorns <a2e5f936c390f36494e46e71bcfbe365bb1e8c49@pengutronix.de>

rauc/rauc,rauc/rauc,jluebbe/rauc,ejoerns/rauc,ejoerns/rauc,rauc/rauc,jluebbe/rauc,ejoerns/rauc,jluebbe/rauc