net: disallow to specify multicast MAC address

[Assigning a multicast MAC address to a NIC leads to confusing behavior.
Reject multicast MAC addresses so users are alerted to their error
straight away.

The "net/eth.h" in6_addr rename prevents a name collision with
<netinet/in.h> on Linux.
-- Stefan]
Signed-off-by: NDmitry V. Krivenok <krivenok.dmitry@gmail.com>
Reviewed-by: Amos Kong <kongjianjun@gmail.com>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

include/net/eth.h

@@ -84,7 +84,7 @@ typedef struct ip_pseudo_header {
 } ip_pseudo_header;
 
 /* IPv6 address */
-struct in6_addr {
+struct in6_address {
     union {
         uint8_t __u6_addr8[16];
     } __in6_u;
@@ -105,8 +105,8 @@ struct ip6_header {
             uint8_t  ip6_un3_ecn;  /* 2 bits ECN, top 6 bits payload length */
         } ip6_un3;
     } ip6_ctlun;
-    struct in6_addr ip6_src;     /* source address */
-    struct in6_addr ip6_dst;     /* destination address */
+    struct in6_address ip6_src;    /* source address */
+    struct in6_address ip6_dst;    /* destination address */
 };
 
 struct ip6_ext_hdr {

net/net.c

@@ -27,6 +27,7 @@
 #include "clients.h"
 #include "hub.h"
 #include "net/slirp.h"
+#include "net/eth.h"
 #include "util.h"
 
 #include "monitor/monitor.h"
@@ -689,6 +690,11 @@ static int net_init_nic(const NetClientOptions *opts, const char *name,
         error_report("invalid syntax for ethernet address");
         return -1;
     }
+    if (nic->has_macaddr &&
+        is_multicast_ether_addr(nd->macaddr.a)) {
+        error_report("NIC cannot have multicast MAC address (odd 1st byte)");
+        return -1;
+    }
     qemu_macaddr_default_if_unset(&nd->macaddr);
 
     if (nic->has_vectors) {