r8169: improve rtl_coalesce_info

tp->coalesce_info is used in rtl_coalesce_info() only, so we can
remove this member. In addition replace phy_ethtool_get_link_ksettings
with a direct access to tp->phydev->speed.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>