[NET]: Add support for getting the permanent hardware address.

This patch adds a new field to net device to hold the permanent
hardware address, and adds a new generic ethtool_op function to
get that address.

Signed-off-by: Jon Wetzel <jon_wetzel@dell.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>