igmp: call IFF_SET_IPv4 when igmp_send

If the flag is not set, The flag is affected by the previously sent and
received packets, L2 header may be filled with ipv6

Signed-off-by: zhanghongyu <zhanghongyu@xiaomi.com>

net/igmp/igmp_send.c

@@ -116,6 +116,10 @@ void igmp_send(FAR struct net_driver_s *dev, FAR struct igmp_group_s *group,
       return;
     }
 
+  /* Select IPv4 */
+
+  IFF_SET_IPv4(dev->d_flags);
+
   /* The IGMP header immediately follows the IP header */
 
   iphdrlen          = IPv4_HDRLEN + RASIZE;