enic: rename CMD_MAC_ADDR to CMD_GET_MAC_ADDR

firmware devcmd CMD_MAC_ADDR gets the mac address of a vnic from adapter.
This patch renames it to CMD_GET_MAC_ADDR more appropriately.

Signed-off-by: Roopa Prabhu <roprabhu@cisco.com>
Signed-off-by: Christian Benvenuti <benve@cisco.com>
Signed-off-by: Sujith Sankar <ssujith@cisco.com>
Signed-off-by: David S. Miller <davem@davemloft.net>