net: ixp4xx_eth: Support changing the MTU
As we don't specify the MTU in the driver, the framework
will fall back to 1500 bytes and this doesn't work very
well when we try to attach a DSA switch:
eth1: mtu greater than device maximum
ixp4xx_eth
c800a000.ethernet eth1: error -22 setting
MTU to 1504 to include DSA overhead
After locating an out-of-tree patch in OpenWrt I found
suitable code to set the MTU on the interface and ported
it and updated it. Now the MTU gets set properly.
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20231005-ixp4xx-eth-mtu-v4-1-08c66ed0bc69@linaro.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>