different PHY instance being selected and isolation out into the wrappers
around the service methods rather than duplicating them over and over
again (besides, a PHY driver shouldn't need to care about which instance
it actually is).
- Centralize the check for the need to isolate a non-zero PHY instance not
supporting isolation in mii_mediachg() and just ignore it rather than
panicing, which should sufficient given that a) things are likely to
just work anyway if one doesn't plug in more than one port at a time and
b) refusing to attach in this case just leaves us in a unknown but most
likely also not exactly correct configuration (besides several drivers
setting MIIF_NOISOLATE didn't care about these anyway, probably due to
setting this flag for no real reason).
- Minor fixes like removing unnecessary setting of sc->mii_anegticks,
using sc->mii_anegticks instead of hardcoded values etc.
