sh_eth: kill useless *switch* defaults

The driver often has the *default* cases doing nothing in the *switch*
statements with  the integer expressions -- remove them.

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: David S. Miller <davem@davemloft.net>