MFC if_re.c 1.73 to RELENG_6.
Make 8139C+ work again which was broken since rev 1.68. Ever since rev 1.68 re(4) checks the validity of link in re_start. But rlphy(4) got a garbled data due to a different bit layout used on 8139C+ and it couldn't report correct link state. To fix it, ignore BMCR_LOOP and BMCR_ISO bits which have different meanings on 8139C+. I think this also make dhclient(8) work on 8139C+.
Approved by: re (mux)