net: ll_temac: Do not make promiscuous mode sticky on multicast

When user has requested IFF_ALLMULTI or have set more than 4 multicast
addresses, we should just use promiscuous mode, but not set it in flags,
as it causes the interface to stay in promiscuous mode even when the
non-IFF_PROMISC condition that caused promiscuous mode to be enabled
has gone away.

Signed-off-by: Esben Haabendal <esben@geanix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>