In this test suite, the actual peer interacting with the TCP stack is
the test suite itself, therefore all test cases should take care to
finalize the underlying TCP connection before ending, not to interfere
with other test cases.
This was not the case for test_server_out_of_order_data(), which
although released the underlying context on their side, did not finalize
the connection at the TCP level, i. e. did not reply for the FIN packet
etc.
As it seems to be unnecessary overhead to implement the full connection
teardown for the test case, simply send a RST packet to abort the
connection at the TCP level before releasing the context.
This was causing occasional failures in this test suite, as the FIN
packets retransmitted by the TCP stack could interfere with other test
cases logic.
Signed-off-by: Robert Lubos <robert.lubos@nordicsemi.no>