netinet6: embed struct nd_ifinfo into struct in6_ndireq

There is no functional change here, but we'd like to emphasize that the
nd_ifinfo structure is not a actually a kernel ND6 software context,
despite being actively used like this way, but an API/ABI structure for
ioctl(2).  This should prevent from a ABI breakages like in 31ec8b6407.
This also is a step towards stopping using it as a kernel software
context.

Reviewed by:		tuexen
Differential Revision:	https://reviews.freebsd.org/D54722

sys/netinet6/nd6.h

@@ -62,22 +62,6 @@ struct llentry;
 #define ND6_IS_LLINFO_PROBREACH(n) ((n)->ln_state > ND6_LLINFO_INCOMPLETE)
 #define ND6_LLINFO_PERMANENT(n) (((n)->la_expire == 0) && ((n)->ln_state > ND6_LLINFO_INCOMPLETE))
 
-struct nd_ifinfo {
-	u_int32_t linkmtu;		/* LinkMTU */
-	u_int32_t maxmtu;		/* Upper bound of LinkMTU */
-	u_int32_t basereachable;	/* BaseReachableTime */
-	u_int32_t reachable;		/* Reachable Time */
-	u_int32_t retrans;		/* Retrans Timer */
-	u_int32_t flags;		/* Flags */
-	int recalctm;			/* BaseReacable re-calculation timer */
-	u_int8_t chlim;			/* CurHopLimit */
-	u_int8_t initialized; /* Flag to see the entry is initialized */
-	/* the following 3 members are for privacy extension for addrconf */
-	u_int8_t randomseed0[8]; /* upper 64 bits of MD5 digest */
-	u_int8_t randomseed1[8]; /* lower 64 bits (usually the EUI64 IFID) */
-	u_int8_t randomid[8];	/* current random ID */
-};
-
 #define ND6_IFF_PERFORMNUD	0x1
 #define ND6_IFF_ACCEPT_RTADV	0x2
 #define ND6_IFF_PREFER_SOURCE	0x4 /* Not used in FreeBSD. */
@@ -139,9 +123,29 @@ struct in6_prefix {
 	/* struct sockaddr_in6 advrtr[] */
 };
 
-struct	in6_ndireq {
+struct in6_ndireq {
 	char ifname[IFNAMSIZ];
-	struct nd_ifinfo ndi;
+	struct nd_ifinfo {
+		uint32_t linkmtu;	/* LinkMTU */
+		uint32_t maxmtu;	/* Upper bound of LinkMTU */
+		uint32_t basereachable;	/* BaseReachableTime */
+		uint32_t reachable;	/* Reachable Time */
+		uint32_t retrans;	/* Retrans Timer */
+		uint32_t flags;		/* Flags */
+		int recalctm;		/* BaseReacable re-calculation timer */
+		uint8_t chlim;		/* CurHopLimit */
+		/*
+		 * The below members are not used.  They came from KAME and
+		 * are hanging around to preserve ABI compatibility of the
+		 * SIOCGIFINFO_IN6 ioctl.
+		 * The original comment documented the random* members as a
+		 * privacy extension for addrconf.
+		 */
+		uint8_t initialized;	/* compat: always 1 */
+		uint8_t randomseed0[8]; /* upper 64 bits of MD5 digest */
+		uint8_t randomseed1[8]; /* lower 64 bits (the EUI64 IFID?) */
+		uint8_t randomid[8];	/* current random ID */
+	} ndi;
 };
 
 struct	in6_ndifreq {