network: introduce ip nexthop routing

Used to manipulate entries in the kernel's nexthop tables.
Example:
```
[NextHop]
Id=3
Gateway=192.168.5.1
```

src/basic/linux/nexthop.h

@@ -0,0 +1,56 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef _LINUX_NEXTHOP_H
+#define _LINUX_NEXTHOP_H
+
+#include <linux/types.h>
+
+struct nhmsg {
+        unsigned char   nh_family;
+        unsigned char   nh_scope;     /* return only */
+        unsigned char   nh_protocol;  /* Routing protocol that installed nh */
+        unsigned char   resvd;
+        unsigned int    nh_flags;     /* RTNH_F flags */
+};
+
+/* entry in a nexthop group */
+struct nexthop_grp {
+        __u32   id;       /* nexthop id - must exist */
+        __u8    weight;   /* weight of this nexthop */
+        __u8    resvd1;
+        __u16   resvd2;
+};
+
+enum {
+      NEXTHOP_GRP_TYPE_MPATH,  /* default type if not specified */
+      __NEXTHOP_GRP_TYPE_MAX,
+};
+
+#define NEXTHOP_GRP_TYPE_MAX (__NEXTHOP_GRP_TYPE_MAX - 1)
+
+enum {
+      NHA_UNSPEC,
+      NHA_ID,           /* u32; id for nexthop. id == 0 means auto-assign */
+
+      NHA_GROUP,        /* array of nexthop_grp */
+      NHA_GROUP_TYPE,   /* u16 one of NEXTHOP_GRP_TYPE */
+      /* if NHA_GROUP attribute is added, no other attributes can be set */
+
+      NHA_BLACKHOLE,    /* flag; nexthop used to blackhole packets */
+      /* if NHA_BLACKHOLE is added, OIF, GATEWAY, ENCAP can not be set */
+
+      NHA_OIF,  /* u32; nexthop device */
+      NHA_GATEWAY,      /* be32 (IPv4) or in6_addr (IPv6) gw address */
+      NHA_ENCAP_TYPE, /* u16; lwt encap type */
+      NHA_ENCAP,        /* lwt encap data */
+
+      /* NHA_OIF can be appended to dump request to return only
+       * nexthops using given device
+       */
+      NHA_GROUPS,       /* flag; only return nexthop groups in dump */
+      NHA_MASTER,       /* u32;  only return nexthops with given master dev */
+
+      __NHA_MAX,
+};
+
+#define NHA_MAX (__NHA_MAX - 1)
+#endif

src/basic/linux/rtnetlink.h

@@ -157,6 +157,13 @@ enum {
 	RTM_GETCHAIN,
 #define RTM_GETCHAIN RTM_GETCHAIN
 
+        RTM_NEWNEXTHOP = 104,
+#define RTM_NEWNEXTHOP	RTM_NEWNEXTHOP
+        RTM_DELNEXTHOP,
+#define RTM_DELNEXTHOP	RTM_DELNEXTHOP
+        RTM_GETNEXTHOP,
+#define RTM_GETNEXTHOP	RTM_GETNEXTHOP
+
 	__RTM_MAX,
 #define RTM_MAX		(((__RTM_MAX + 3) & ~3) - 1)
 };
@@ -165,7 +172,7 @@ enum {
 #define RTM_NR_FAMILIES	(RTM_NR_MSGTYPES >> 2)
 #define RTM_FAM(cmd)	(((cmd) - RTM_BASE) >> 2)
 
-/* 
+/*
    Generic structure for encapsulation of optional route information.
    It is reminiscent of sockaddr, but with sa_family replaced
    with attribute type.
@@ -205,7 +212,7 @@ struct rtmsg {
 
 	unsigned char		rtm_table;	/* Routing table id */
 	unsigned char		rtm_protocol;	/* Routing protocol; see below	*/
-	unsigned char		rtm_scope;	/* See below */	
+        unsigned char		rtm_scope;	/* See below */
 	unsigned char		rtm_type;	/* See below	*/
 
 	unsigned		rtm_flags;
@@ -342,6 +349,7 @@ enum rtattr_type_t {
 	RTA_IP_PROTO,
 	RTA_SPORT,
 	RTA_DPORT,
+        RTA_NH_ID,
 	__RTA_MAX
 };
 
@@ -515,7 +523,7 @@ struct ifinfomsg {
 };
 
 /********************************************************************
- *		prefix information 
+ *		prefix information
  ****/
 
 struct prefixmsg {
@@ -529,7 +537,7 @@ struct prefixmsg {
 	unsigned char	prefix_pad3;
 };
 
-enum 
+enum
 {
 	PREFIX_UNSPEC,
 	PREFIX_ADDRESS,
@@ -704,6 +712,8 @@ enum rtnetlink_groups {
 #define RTNLGRP_IPV4_MROUTE_R	RTNLGRP_IPV4_MROUTE_R
 	RTNLGRP_IPV6_MROUTE_R,
 #define RTNLGRP_IPV6_MROUTE_R	RTNLGRP_IPV6_MROUTE_R
+        RTNLGRP_NEXTHOP,
+#define RTNLGRP_NEXTHOP		RTNLGRP_NEXTHOP
 	__RTNLGRP_MAX
 };
 #define RTNLGRP_MAX	(__RTNLGRP_MAX - 1)