bnxt_en: enforce proper storing of MAC address

For PF, the bp->pf.mac_addr always holds the permanent MAC
addr assigned by the HW.  For VF, the bp->vf.mac_addr always
holds the administrator assigned VF MAC addr. The random
generated VF MAC addr should never get stored to bp->vf.mac_addr.
This way, when the VF wants to change the MAC address, we can tell
if the adminstrator has already set it and disallow the VF from
changing it.

v2: Fix compile error if CONFIG_BNXT_SRIOV is not set.

Signed-off-by: Jeffrey Huang <huangjw@broadcom.com>
Signed-off-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>