net: phy-c45: Fix genphy_c45_ethtool_set_eee description

The text has been cut/paste from genphy_c45_ethtool_get_eee but not
changed to reflect it performs set.

Additionally, extend the comment. This function implements the logic
that eee_enabled has global control over EEE. When eee_enabled is
false, no link modes will be advertised, and as a result, the MAC
should not transmit LPI.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Link: https://lore.kernel.org/r/20230619220332.4038924-1-andrew@lunn.ch


Signed-off-by: Jakub Kicinski <kuba@kernel.org>