Documentation: net: dsa: Cut set_addr() documentation

This is not supported anymore, devices needing a MAC address
just assign one at random, it's just a driver pecularity.
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/networking/dsa/dsa.txt

@@ -385,11 +385,6 @@ Switch configuration
   avoid relying on what a previous software agent such as a bootloader/firmware
   may have previously configured.
 
-- set_addr: Some switches require the programming of the management interface's
-  Ethernet MAC address, switch drivers can also disable ageing of MAC addresses
-  on the management interface and "hardcode"/"force" this MAC address for the
-  CPU/management interface as an optimization
-
 PHY devices and link management
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