Make kobject_set_name_vargs() do nothing on <= 2.6.24

Make kobject_set_name_vargs() do nothing on <= 2.6.24

The struct kobject does not have a name member on older kernels
so naming something naming a kobject will be futile. This implies
dev_set_name() won't be able to rename the kobject. This may
actually bust 2.6.24, I believe we discussed this particular
issue on the linux-wireless mailing list at some point with
a person trying 2.6.24. If there is an issue with this patch
we can go back and check the list. I'm offline rigtt now though
so trying to get compilation to work at least.

Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>