Documentation: networking: Add missing PHY_GET command in the message list

ETHTOOL_MSG_PHY_GET/GET_REPLY/NTF is missing in the ethtool message list.
Add it to the ethool netlink documentation.

Signed-off-by: Kory Maincent <kory.maincent@bootlin.com>
Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Link: https://patch.msgid.link/20241028132351.75922-1-kory.maincent@bootlin.com


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