ehea: Fix multicast registration on semi-promiscuous mode

Ehea will not register multicast groups in phyp if the physical
interface is in promiscuous mode. But it should register if the
logical port is in promiscuous mode, but the physical port is not.

Ehea physical promiscuous mode is defined by ehea_port->promisc,
while logical port is defined by IFF_PROMISC.

So currently, if the user set the interface in promiscuous mode,
IGMP will not be registred in PHYP, and PHYP will never pass
the multicast packet to the logical port, which is bad

So, this patch just fixes it, assuring that we register in phyp
if the physical port is not on promiscuous mode.

Signed-off-by: Breno Leitao <leitao@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>