be2net: fix initial MAC setting

Recent commit 34393529 ("be2net: fix MAC addr setting on privileged
BE3 VFs") allows privileged BE3 VFs to set its MAC address during
initialization. Although the initial MAC for such VFs is already
programmed by parent PF the subsequent setting performed by VF is OK,
but in certain cases (after fresh boot) this command in VF can fail.

The MAC should be initialized only when:
1) no MAC is programmed (always except BE3 VFs during first init)
2) programmed MAC is different from requested (e.g. MAC is set when
   interface is down). In this case the initial MAC programmed by PF
   needs to be deleted.

The adapter->dev_mac contains MAC address currently programmed in HW so
it should be zeroed when the MAC is deleted from HW and should not be
filled when MAC is set when interface is down in be_mac_addr_set() as
no programming is performed in this case.

Example of failure without the fix (immediately after fresh boot):

# ip link set eth0 up  <- eth0 is BE3 PF
be2net 0000:01:00.0 eth0: Link is Up

# echo 1 > /sys/class/net/eth0/device/sriov_numvfs  <- Create 1 VF
...
be2net 0000:01:04.0: Emulex OneConnect(be3): VF  port 0

# ip link set eth8 up  <- eth8 is created privileged VF
be2net 0000:01:04.0: opcode 59-1 failed:status 1-76
RTNETLINK answers: Input/output error

# echo 0 > /sys/class/net/eth0/device/sriov_numvfs  <- Delete VF
iommu: Removing device 0000:01:04.0 from group 33
...

# echo 1 > /sys/class/net/eth0/device/sriov_numvfs  <- Create it again
iommu: Removing device 0000:01:04.0 from group 33
...

# ip link set eth8 up
be2net 0000:01:04.0 eth8: Link is Up

Initialization is now OK.

v2 - Corrected the comment and condition check suggested by Suresh & Harsha

Fixes: 34393529 ("be2net: fix MAC addr setting on privileged BE3 VFs")
Cc: Sathya Perla <sathya.perla@broadcom.com>
Cc: Ajit Khaparde <ajit.khaparde@broadcom.com>
Cc: Sriharsha Basavapatna <sriharsha.basavapatna@broadcom.com>
Cc: Somnath Kotur <somnath.kotur@broadcom.com>
Signed-off-by: Ivan Vecera <cera@cera.cz>
Acked-by: Sriharsha Basavapatna <sriharsha.basavapatna@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>