config: restore PHYLIB=m
    
    This essentially reverts kernel-source commit fcc47b444be6 ("config:
    enable PHYLIB=y and ETHTOOL_NETLINK=y") which responded to upstream
    change not allowing ETHTOOL_NETLINK=y with PHYLIB=m. There are two
    exceptions:
    
      - vanilla flavors keep PHYLIB=y as patches fixing the dependency are
        not applied to */vanilla (will be fixed with 5.9-rc1 update)
      - we preserve ETHTOOL_NETLINK=y which was previously lost in 5.8-rc1
        update