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 <[e-mail]>
Reviewed-by: Maxime Chevallier <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Jakub Kicinski <[e-mail]>

Documentation/networking/ethtool-netlink.rst

···
   ``ETHTOOL_MSG_MM_GET``                get MAC merge layer state
   ``ETHTOOL_MSG_MM_SET``                set MAC merge layer parameters
   ``ETHTOOL_MSG_MODULE_FW_FLASH_ACT``   flash transceiver module firmware
+  ``ETHTOOL_MSG_PHY_GET``               get Ethernet PHY information
   ===================================== =================================
 
 Kernel to userspace:
···
   ``ETHTOOL_MSG_PLCA_NTF``                 PLCA RS parameters
   ``ETHTOOL_MSG_MM_GET_REPLY``             MAC merge layer status
   ``ETHTOOL_MSG_MODULE_FW_FLASH_NTF``      transceiver module flash updates
+  ``ETHTOOL_MSG_PHY_GET_REPLY``            Ethernet PHY information
+  ``ETHTOOL_MSG_PHY_NTF``                  Ethernet PHY information change
   ======================================== =================================
 
 ``GET`` requests are sent by userspace applications to retrieve device