fix pf_get_rdr() for single port (dport2 == 0) rules. found by lebel@.
fix pf_get_rdr() for single port (dport2 == 0) rules. found by lebel@.

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