engine: more checks on IPv6 and multicast

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/engines/net.c b/engines/net.c
index 5fdc88c..4be106a 100644
--- a/engines/net.c
+++ b/engines/net.c
@@ -1039,12 +1039,17 @@
 	}
 #endif
 
-	if (td->o.filename){
+	if (td->o.filename) {
 		if (!is_udp(o) || !fio_netio_is_multicast(td->o.filename)) {
 			log_err("fio: hostname not valid for non-multicast inbound network IO\n");
 			close(fd);
 			return 1;
 		}
+		if (is_ipv6(o)) {
+			log_err("fio: IPv6 not supported for multicast network IO");
+			close(fd);
+			return 1;
+		}
 
 		inet_aton(td->o.filename, &sin.sin_addr);
 
@@ -1058,6 +1063,7 @@
 		} else {
 			mr.imr_interface.s_addr = htonl(INADDR_ANY);
 		}
+
 		if (setsockopt(fd, IPPROTO_IP, IP_ADD_MEMBERSHIP, (const char*)&mr, sizeof(mr)) < 0) {
 			td_verror(td, errno, "setsockopt IP_ADD_MEMBERSHIP");
 			close(fd);