be2net: Prevent VFs from enabling VLAN promiscuous mode

Currently, a PF does not restrict its VF interface from enabling vlan
promiscuous mode. This breaks vlan isolation when a vlan
(transparent tagging) is configured on a VF.

This patch fixes this problem by disabling the vlan promisc capability
for VFs.

Reported-by: Yoann Juet <veilletechno-irts@univ-nantes.fr>
Signed-off-by: Vasundhara Volam <vasundhara.volam@emulex.com>
Signed-off-by: Sathya Perla <sathya.perla@emulex.com>
Signed-off-by: David S. Miller <davem@davemloft.net>