bpf: test ref bit from data path and add new tests for syscall path

The test_lru_map is relying on marking the LRU map entry via regular
BPF map lookup from system call side. This is basically for simplicity
reasons. Given we fixed marking entries in that case, the test needs
to be fixed as well. Here we add a small drop-in replacement to retain
existing behavior for the tests by marking out of the BPF program and
transferring the retrieved value out via temporary map. This also adds
new test cases to track the new behavior where two elements are marked,
one via system call side and one via program side, where the next update
then evicts the key looked up only from system call side.

  # ./test_lru_map
  nr_cpus:8

  test_lru_sanity0 (map_type:9 map_flags:0x0): Pass
  test_lru_sanity1 (map_type:9 map_flags:0x0): Pass
  test_lru_sanity2 (map_type:9 map_flags:0x0): Pass
  test_lru_sanity3 (map_type:9 map_flags:0x0): Pass
  test_lru_sanity4 (map_type:9 map_flags:0x0): Pass
  test_lru_sanity5 (map_type:9 map_flags:0x0): Pass
  test_lru_sanity7 (map_type:9 map_flags:0x0): Pass
  test_lru_sanity8 (map_type:9 map_flags:0x0): Pass

  test_lru_sanity0 (map_type:10 map_flags:0x0): Pass
  test_lru_sanity1 (map_type:10 map_flags:0x0): Pass
  test_lru_sanity2 (map_type:10 map_flags:0x0): Pass
  test_lru_sanity3 (map_type:10 map_flags:0x0): Pass
  test_lru_sanity4 (map_type:10 map_flags:0x0): Pass
  test_lru_sanity5 (map_type:10 map_flags:0x0): Pass
  test_lru_sanity7 (map_type:10 map_flags:0x0): Pass
  test_lru_sanity8 (map_type:10 map_flags:0x0): Pass

  test_lru_sanity0 (map_type:9 map_flags:0x2): Pass
  test_lru_sanity4 (map_type:9 map_flags:0x2): Pass
  test_lru_sanity6 (map_type:9 map_flags:0x2): Pass
  test_lru_sanity7 (map_type:9 map_flags:0x2): Pass
  test_lru_sanity8 (map_type:9 map_flags:0x2): Pass

  test_lru_sanity0 (map_type:10 map_flags:0x2): Pass
  test_lru_sanity4 (map_type:10 map_flags:0x2): Pass
  test_lru_sanity6 (map_type:10 map_flags:0x2): Pass
  test_lru_sanity7 (map_type:10 map_flags:0x2): Pass
  test_lru_sanity8 (map_type:10 map_flags:0x2): Pass
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>