app/test: fix IPv6 header initialization

Fix two issues found when writing PMD unit tests for HW ptype and
L4 checksum offload:

   - The version field in the IPv6 header was being set to zero,
     which prevented hardware from recognizing it as IPv6. The
     IP version field is now set to six.
   - The payload_len field was being initialized using host byte
     order, which (among other things) resulted in incorrect L4
     checksum computation. The payload_len field is now set using
     network (big-endian) byte order.

Fixes: 92073ef ("bond: unit tests")
Cc: stable@dpdk.org

Signed-off-by: Lance Richardson <lance.richardson@broadcom.com>
Reviewed-by: David Marchand <david.marchand@redhat.com>

app/test/packet_burst_generator.c

@@ -142,8 +142,8 @@ uint16_t
 initialize_ipv6_header(struct rte_ipv6_hdr *ip_hdr, uint8_t *src_addr,
 		uint8_t *dst_addr, uint16_t pkt_data_len)
 {
-	ip_hdr->vtc_flow = 0;
-	ip_hdr->payload_len = pkt_data_len;
+	ip_hdr->vtc_flow = rte_cpu_to_be_32(0x60000000); /* Set version to 6. */
+	ip_hdr->payload_len = rte_cpu_to_be_16(pkt_data_len);
 	ip_hdr->proto = IPPROTO_UDP;
 	ip_hdr->hop_limits = IP_DEFTTL;