[NET]: Return more appropriate error from eth_validate_addr().

Paul Bolle wrote:
> http://bugzilla.kernel.org/show_bug.cgi?id=9923 would have been much easier to
> track down if eth_validate_addr() would somehow complain aloud if an address 
> is invalid. Shouldn't it make at least some noise?

I guess it should return -EADDRNOTAVAIL similar to eth_mac_addr()
when validation fails.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>