bpf_base_test - usleep sleeps microseconds not miliseconds

Fix some
  netd_integration_test32.BpfBasicTest#TestCloseSocketWithoutUntag
flakiness:
  system/netd/tests/bpf_base_test.cpp:144: Failure
  Failed
  socket tag still exist after 500ms

Test: atest libbpf_android_test libnetdbpf_test netd_integration_test netd_unit_test netdutils_test resolv_integration_test resolv_unit_test
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I311d6acff1d2d34235169a30c6dc8ff14a361499