forcedeth: mac address mcp77/79

This patch is a critical fix for MCP77 and MCP79 devices. The feature
flags were missing the define for correct mac address
(DEV_HAS_CORRECT_MACADDR).

Signed-off-by: Ayaz Abdulla <aabdulla@nvidia.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>
Signed-off-by: David S. Miller <davem@davemloft.net>