Reland floss: Add unittests for btm_sco_hci

Fix the flaky ScoHciWithOpenCleanTest#ScoOverHciWrite that requires
mock_uipc_send_ret to be set to True by calling the ScoHciTest::SetUp
in the ScoHciWithOpenCleanTest::SetUp.

Bug: 232463744
Tag: #floss
Test: atest --host net_test_stack_btm:ScoHciWithOpenCleanTest.ScoOverHciWrite
--no-bazel-mode --iterations to verify the flaky test passed.

Change-Id: Ic0431490cfa7cd88d8957d22b746519ca1c6f564