sync BPF compat headers with latest bpf-next, update BPF features list

Update doc/kernel-versions.md with latest eBPF features, map types,
JIT-compiler, helpers.

Synchronise headers with bpf-next (at commit bcece5dc40b9). Add
prototypes for the following helpers:

- bpf_get_stack()
- bpf_skb_load_bytes_relative()
- bpf_fib_lookup()
- bpf_sock_hash_update()
- bpf_msg_redirect_hash()
- bpf_sk_redirect_hash()
- bpf_lwt_push_encap()
- bpf_lwt_seg6_store_bytes()
- bpf_lwt_seg6_adjust_srh()
- bpf_lwt_seg6_action()
- bpf_rc_repeat()
- bpf_rc_keydown()

src/cc/export/helpers.h

@@ -356,6 +356,30 @@ static int (*bpf_xdp_adjust_tail)(void *ctx, int offset) =
   (void *) BPF_FUNC_xdp_adjust_tail;
 static int (*bpf_skb_get_xfrm_state)(void *ctx, u32 index, void *xfrm_state, u32 size, u64 flags) =
   (void *) BPF_FUNC_skb_get_xfrm_state;
+static int (*bpf_get_stack)(void *ctx, void *buf, u32 size, u64 flags) =
+  (void *) BPF_FUNC_get_stack;
+static int (*bpf_skb_load_bytes_relative)(void *ctx, u32 offset, void *to, u32 len, u32 start_header) =
+  (void *) BPF_FUNC_skb_load_bytes_relative;
+static int (*bpf_fib_lookup)(void *ctx, void *params, int plen, u32 flags) =
+  (void *) BPF_FUNC_fib_lookup;
+static int (*bpf_sock_hash_update)(void *ctx, void *map, void *key, u64 flags) =
+  (void *) BPF_FUNC_sock_hash_update;
+static int (*bpf_msg_redirect_hash)(void *ctx, void *map, void *key, u64 flags) =
+  (void *) BPF_FUNC_msg_redirect_hash;
+static int (*bpf_sk_redirect_hash)(void *ctx, void *map, void *key, u64 flags) =
+  (void *) BPF_FUNC_sk_redirect_hash;
+static int (*bpf_lwt_push_encap)(void *skb, u32 type, void *hdr, u32 len) =
+  (void *) BPF_FUNC_lwt_push_encap;
+static int (*bpf_lwt_seg6_store_bytes)(void *ctx, u32 offset, const void *from, u32 len) =
+  (void *) BPF_FUNC_lwt_seg6_store_bytes;
+static int (*bpf_lwt_seg6_adjust_srh)(void *ctx, u32 offset, s32 delta) =
+  (void *) BPF_FUNC_lwt_seg6_adjust_srh;
+static int (*bpf_lwt_seg6_action)(void *ctx, u32 action, void *param, u32 param_len) =
+  (void *) BPF_FUNC_lwt_seg6_action;
+static int (*bpf_rc_keydown)(void *ctx, u32 protocol, u64 scancode, u32 toggle) =
+  (void *) BPF_FUNC_rc_keydown;
+static int (*bpf_rc_repeat)(void *ctx) =
+  (void *) BPF_FUNC_rc_repeat;
 
 /* llvm builtin functions that eBPF C program may use to
  * emit BPF_LD_ABS and BPF_LD_IND instructions

src/cc/libbpf.c

@@ -156,6 +156,18 @@ static struct bpf_helper helpers[] = {
   {"bind", "4.17"},
   {"xdp_adjust_tail", "4.18"},
   {"skb_get_xfrm_state", "4.18"},
+  {"get_stack", "4.18"},
+  {"skb_load_bytes_relative", "4.18"},
+  {"fib_lookup", "4.18"},
+  {"sock_hash_update", "4.18"},
+  {"msg_redirect_hash", "4.18"},
+  {"sk_redirect_hash", "4.18"},
+  {"lwt_push_encap", "4.18"},
+  {"lwt_seg6_store_bytes", "4.18"},
+  {"lwt_seg6_adjust_srh", "4.18"},
+  {"lwt_seg6_action", "4.18"},
+  {"rc_repeat", "4.18"},
+  {"rc_keydown", "4.18"},
 };
 
 static uint64_t ptr_to_u64(void *ptr)