net: ethernet: Fix the multicast IPv4 to MAC address mapping

The IPv4 multicast address to MAC address mapping was missing
the 4th byte high bit clearing.

We also need to have some storage for the multicast MAC address.
This was missing which could cause NULL pointer access.

Signed-off-by: Jukka Rissanen <jukka.rissanen@linux.intel.com>

Author: jukkar

subsys/net/ip/l2/ethernet.c

@@ -170,6 +170,8 @@ static inline bool check_if_dst_is_broadcast_or_mcast(struct net_if *iface,
 		hdr->dst.addr[4] = NET_IPV4_HDR(pkt)->dst.s4_addr[2];
 		hdr->dst.addr[5] = NET_IPV4_HDR(pkt)->dst.s4_addr[3];
 
+		hdr->dst.addr[3] = hdr->dst.addr[3] & 0x7f;
+
 		net_pkt_ll_dst(pkt)->len = sizeof(struct net_eth_addr);
 		net_pkt_ll_src(pkt)->addr = net_if_get_link_addr(iface)->addr;
 		net_pkt_ll_src(pkt)->len = sizeof(struct net_eth_addr);
@@ -192,6 +194,9 @@ static enum net_verdict ethernet_send(struct net_if *iface,
 		struct net_pkt *arp_pkt;
 
 		if (check_if_dst_is_broadcast_or_mcast(iface, pkt)) {
+			struct net_eth_addr *dst = &NET_ETH_HDR(pkt)->dst;
+
+			net_pkt_ll_dst(pkt)->addr = (u8_t *)dst->addr;
 			goto setup_hdr;
 		}