ehea: fix promiscuous mode

commit a4910b74

 has broken promiscuous
mode, which is never set. port->promisc just reflects the last setting
of PROMISCUOUS mode to avoid doing an extra hypercall when it's already
set.

However, since it may fail because of hypervisor permissions, we should
still respect the multicast settings and not simply exit after setting
promiscuous mode.

Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@linux.vnet.ibm.com>
Cc: Breno Leitao <leitao@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>