Enable calling map_update_elem on sockmaps from bpf_iter context. This
in turn allows us to copy a sockmap by iterating its elements.

The change itself is tiny, all thanks to the ground work from Martin,
whose series [1] this patch is based on. I updated the tests to do some
copying, and also included two cleanups.

I'm sending this out now rather than when Martin's series has landed
because I hope this can get in before the merge window (potentially)
closes this weekend.

1: https://lore.kernel.org/bpf/20200925000337.3853598-1-kafai@fb.com/ (local)

Lorenz Bauer (4):
  bpf: sockmap: enable map_update_elem from bpf_iter
  selftests: bpf: Add helper to compare socket cookies
  bpf: selftests: remove shared header from sockmap iter test
  selftest: bpf: Test copying a sockmap and sockhash

 kernel/bpf/verifier.c                         |   2 +-
 net/core/sock_map.c                           |   3 +
 .../selftests/bpf/prog_tests/sockmap_basic.c  | 100 +++++++++++-------
 .../selftests/bpf/progs/bpf_iter_sockmap.c    |  32 ++++--
 .../selftests/bpf/progs/bpf_iter_sockmap.h    |   3 -
 5 files changed, 90 insertions(+), 50 deletions(-)
 delete mode 100644 tools/testing/selftests/bpf/progs/bpf_iter_sockmap.h

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2.25.1