[PATCH v4] net: add bit fields to IPv6 header definition

[Gregory Etelson <getelson@nvidia.com>]

DPDK IPv6 header definition combined the `version`, `traffic class`
and `flow label` header fields into a single 32 bits structure member
`vtc_flow`.

The patch expands IPv6 header definition with dedicated structure
members for the `version`, `traffic class` and `flow label` fields.
The `traffic class` is also separated into DS and ECN fields.

The patch also preserves existing `vtc_flow` structure member for
backward compatibility.

Signed-off-by: Gregory Etelson <getelson@nvidia.com>
---
v2: 
Replace uint32_t with rte_be32_t.
Split traffic_class into DS and ECN bits.
v3:
Define both traffic_class and DS + ECN fields.
v4: 
The `packed` attribute works on bytes only.
Back to v2.
---
 lib/net/rte_ip.h | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/lib/net/rte_ip.h b/lib/net/rte_ip.h
index 0d103d4127..fe1d596054 100644
--- a/lib/net/rte_ip.h
+++ b/lib/net/rte_ip.h
@@ -524,7 +524,23 @@ rte_ipv4_udptcp_cksum_mbuf_verify(const struct rte_mbuf *m,
  * IPv6 Header
  */
 struct rte_ipv6_hdr {
-	rte_be32_t vtc_flow;	/**< IP version, traffic class & flow label. */
+	union {
+		rte_be32_t vtc_flow;        /**< IP version, traffic class & flow label. */
+		__extension__
+		struct {
+#if RTE_BYTE_ORDER == RTE_LITTLE_ENDIAN
+			rte_be32_t flow_label:20; /**< flow label */
+			rte_be32_t ecn:2; /**< ECN */
+			rte_be32_t ds:6;     /**< differentiated services */
+			rte_be32_t version:4; /**< version */
+#elif RTE_BYTE_ORDER == RTE_BIG_ENDIAN
+			rte_be32_t version:4; /**< version */
+			rte_be32_t ds:6;     /**< differentiated services */
+			rte_be32_t ecn:2; /**< ECN */
+			rte_be32_t flow_label:20; /**< flow label */
+#endif
+		};
+	};
 	rte_be16_t payload_len;	/**< IP payload size, including ext. headers */
 	uint8_t  proto;		/**< Protocol, next header. */
 	uint8_t  hop_limits;	/**< Hop limits. */
-- 
2.43.0