bnxt_en: Call firmware to approve the random VF MAC address.

After generating the random MAC address for VF, call the firmware to
approve it.  This step serves 2 purposes.  Some hypervisor (e.g. ESX)
wants to approve the MAC address.  2nd, the call will setup the
proper forwarding database in the internal switch.

We need to unlock the hwrm_cmd_lock mutex before calling bnxt_approve_mac().
We can do that because we are at the end of the function and all the
previous firmware response data has been copied.

Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>