Documentation: networking: dsa: Remove poll_link description

This function has been removed in 4baee937b8 ("net: dsa: remove DSA
link polling") in favor of using the PHYLIB polling mechanism.

Reviewed-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/dsa/dsa.txt

@@ -416,11 +416,6 @@ PHY devices and link management
   to the switch port MDIO registers. If unavailable return a negative error
   code.
 
-- poll_link: Function invoked by DSA to query the link state of the switch
-  builtin Ethernet PHYs, per port. This function is responsible for calling
-  netif_carrier_{on,off} when appropriate, and can be used to poll all ports in a
-  single call. Executes from workqueue context.
-
 - adjust_link: Function invoked by the PHY library when a slave network device
   is attached to a PHY device. This function is responsible for appropriately
   configuring the switch port link parameters: speed, duplex, pause based on