net: stmmac: xgmac: fix missing IFF_MULTICAST checki in dwxgmac2_set_filter

Without checking for IFF_MULTICAST flag, it is wrong to assume multicast
filtering is always enabled. By checking against IFF_MULTICAST, now
the driver behaves correctly when the multicast support is toggled by below
command:-
  ip link set <devname> multicast off|on

Fixes: 0efedbf1 ("net: stmmac: xgmac: Fix XGMAC selftests")
Signed-off-by: Tan, Tee Min <tee.min.tan@intel.com>
Signed-off-by: Ong Boon Leong <boon.leong.ong@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/stmicro/stmmac/dwxgmac2_core.c

@@ -458,7 +458,7 @@ static void dwxgmac2_set_filter(struct mac_device_info *hw,
 
 		for (i = 0; i < XGMAC_MAX_HASH_TABLE; i++)
 			writel(~0x0, ioaddr + XGMAC_HASH_TABLE(i));
-	} else if (!netdev_mc_empty(dev)) {
+	} else if (!netdev_mc_empty(dev) && (dev->flags & IFF_MULTICAST)) {
 		struct netdev_hw_addr *ha;
 
 		value |= XGMAC_FILTER_HMC;