INTERNAL: net: dsa: Inherit dev addr from master

When we create slave netdevice, the dev addr is inherited from master
but the master dev addr maybe null at that time, so inherit it again
here.

Signed-off-by: xiaofeis <xiaofeis@codeaurora.org>
Signed-off-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Khasim Syed Mohammed <khasim.mohammed@linaro.org>