Revert "brcompat: Don't re-read configuration file from inside bridge code."

Revert "brcompat: Don't re-read configuration file from inside bridge code."

This reverts commit 2b34f542b1015b69c589bc4fa324d236cd35dd5f, because
not re-reading the config file from phy_port_changed() meant that, later,
the next time we modified the config file we would do it based on the
older version, not the version that we just wrote out.