Issue #243: race in qdr_close_connection_CT

[jiridanek]

WARNING: ThreadSanitizer: data race (pid=3244)
  Write of size 1 at 0x7b54000c9942 by thread T1:
    #0 qdr_close_connection_CT src/router_core/connections.c:267 (skrouterd+0x4875d8)
    #1 qdr_core_close_connection_CT src/router_core/connections.c:283 (skrouterd+0x487766)
    #2 router_core_thread src/router_core/router_core_thread.c:236 (skrouterd+0x4a382a)
    #3 _thread_init src/posix/threading.c:172 (skrouterd+0x47ad5d)

  Previous read of size 1 at 0x7b54000c9942 by main thread:
    #0 qdr_connection_process src/router_core/connections.c:308 (skrouterd+0x48783c)
    #1 _do_reconnect src/adaptors/http1/http1_server.c:432 (skrouterd+0x43bfcc)
    #2 qd_timer_visit src/timer.c:320 (skrouterd+0x4c587f)
    #3 handle src/server.c:980 (skrouterd+0x4c114e)
    #4 thread_run src/server.c:1095 (skrouterd+0x4c2f57)
    #5 qd_server_run src/server.c:1491 (skrouterd+0x4c3acc)
    #6 main_process router/src/main.c:105 (skrouterd+0x424e5c)
    #7 main router/src/main.c:359 (skrouterd+0x4242ec)

  Location is heap block of size 640 at 0x7b54000c9900 allocated by thread T4:
    #0 posix_memalign <null> (libtsan.so.0+0x32a23)
    #1 qd_alloc src/alloc_pool.c:396 (skrouterd+0x448d09)
    #2 new_qdr_connection_t src/router_core/connections.c:44 (skrouterd+0x486d21)
    #3 qdr_connection_opened src/router_core/connections.c:88 (skrouterd+0x486d21)
    #4 _setup_client_connection src/adaptors/http1/http1_client.c:316 (skrouterd+0x4342da)
    #5 _handle_connection_events src/adaptors/http1/http1_client.c:452 (skrouterd+0x4342da)
    #6 handle_event_with_context src/server.c:780 (skrouterd+0x4c11f9)
    #7 do_handle_raw_connection_event src/server.c:786 (skrouterd+0x4c11f9)
    #8 handle src/server.c:1063 (skrouterd+0x4c11f9)
    #9 thread_run src/server.c:1095 (skrouterd+0x4c2f57)
    #10 _thread_init src/posix/threading.c:172 (skrouterd+0x47ad5d)

[jiridanek]

I did not think very hard if this is the correct lock to use. It seemed conveniently placed, so I just extended what it protects by a few lines up. Actually, the closed flag seems to be tightly bound to the list of links with work, so it may make good sense this way, in fact.

[jiridanek]

@kgiusti approved this and the issue has manifested on GHA in controlled environment; therefore, issue is real and fix should be acceptable!