sync: latest libbpf changes from kernel

Syncing latest libbpf commits from kernel repository.
Baseline bpf-next commit:   86ce322d21eb032ed8fdd294d0fb095d2debb430
Checkpoint bpf-next commit: 303dcc25b5c782547eb13b9f29426de843dd6f34
Baseline bpf commit:        78031381ae9c88f4f914d66154f4745122149c58
Checkpoint bpf commit:      6185266c5a853bb0f2a459e3ff594546f277609b

Alexei Starovoitov (1):
  bpf: Count the number of times recursion was prevented

Florent Revest (2):
  bpf: Be less specific about socket cookies guarantees
  bpf: Expose bpf_get_socket_cookie to tracing programs

Hangbin Liu (1):
  bpf: Remove blank line in bpf helper description comment

Jesper Dangaard Brouer (2):
  bpf: bpf_fib_lookup return MTU value as output when looked up
  bpf: Add BPF-helper for MTU checking

Jonas Bonn (1):
  Revert "GTP: add support for flow based tunneling API"

Martin KaFai Lau (1):
  libbpf: Ignore non function pointer member in struct_ops

Stanislav Fomichev (1):
  libbpf: Use AF_LOCAL instead of AF_INET in xsk.c

Yonghong Song (3):
  bpf: Add bpf_for_each_map_elem() helper
  libbpf: Move function is_ldimm64() earlier in libbpf.c
  libbpf: Support subprog address relocation

 include/uapi/linux/bpf.h     | 140 +++++++++++++++++++++++++++++++++--
 include/uapi/linux/if_link.h |   1 -
 src/libbpf.c                 |  98 +++++++++++++++++++-----
 src/xsk.c                    |   2 +-
 4 files changed, 213 insertions(+), 28 deletions(-)

--
2.24.1

BPF-CHECKPOINT-COMMIT

@@ -1 +1 @@
-78031381ae9c88f4f914d66154f4745122149c58
+6185266c5a853bb0f2a459e3ff594546f277609b

CHECKPOINT-COMMIT

@@ -1 +1 @@
-86ce322d21eb032ed8fdd294d0fb095d2debb430
+303dcc25b5c782547eb13b9f29426de843dd6f34