If a caller is requesting to be set to the same rtable that they currently have, let the call succeede.
If a caller is requesting to be set to the same rtable that they
currently have, let the call succeede.

Mirrors the same behaviour as setrtable()

OK claudio@

orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars