netfilter: conntrack: add support for DCCP handshake sequence to ctnetlink

This patch adds CTA_PROTOINFO_DCCP_HANDSHAKE_SEQ that exposes
the u64 handshake sequence number to user-space.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Patrick McHardy <kaber@trash.net>

include/net/netlink.h

@@ -939,6 +939,15 @@ static inline u64 nla_get_u64(const struct nlattr *nla)
 	return tmp;
 }
 
+/**
+ * nla_get_be64 - return payload of __be64 attribute
+ * @nla: __be64 netlink attribute
+ */
+static inline __be64 nla_get_be64(const struct nlattr *nla)
+{
+	return *(__be64 *) nla_data(nla);
+}
+
 /**
  * nla_get_flag - return payload of flag attribute
  * @nla: flag netlink attribute