qdr_link_t->detach_received flag race

Race between I/O thread and Core over reading/writing the qdr_link_t->detach_received flag:

-DCMAKE_BUILD_TYPE=RelWithDebInfo
-DRUNTIME_CHECK=tsan
ctest -V -R system_tests_one_router:

21: WARNING: ThreadSanitizer: data race (pid=14179)
21: Read of size 1 at 0x7b540012c172 by thread T3 (mutexes: write M548167088305615232):
21: #0 qdr_connection_process /home/travis/build/apache/qpid-dispatch/src/router_core/connections.c:441 (libqpid-dispatch.so+0xa81a7)
21: #1 AMQP_writable_conn_handler /home/travis/build/apache/qpid-dispatch/src/router_node.c:299 (libqpid-dispatch.so+0xe3e41)
21: #2 writable_handler /home/travis/build/apache/qpid-dispatch/src/container.c:395 (libqpid-dispatch.so+0x76264)
21: #3 qd_container_handle_event /home/travis/build/apache/qpid-dispatch/src/container.c:747 (libqpid-dispatch.so+0x76264)
21: #4 handle /home/travis/build/apache/qpid-dispatch/src/server.c:1096 (libqpid-dispatch.so+0xed0f1)
21: #5 thread_run /home/travis/build/apache/qpid-dispatch/src/server.c:1121 (libqpid-dispatch.so+0xf0a9c)
21: #6 _thread_init /home/travis/build/apache/qpid-dispatch/src/posix/threading.c:172 (libqpid-dispatch.so+0x96f56)
21: #7 <null> <null> (libtsan.so.0+0x2d1af)

21: Previous write of size 1 at 0x7b540012c172 by thread T1:
21: #0 qdr_link_inbound_detach_CT /home/travis/build/apache/qpid-dispatch/src/router_core/connections.c:1980 (libqpid-dispatch.so+0xad1eb)
21: #1 router_core_thread /home/travis/build/apache/qpid-dispatch/src/router_core/router_core_thread.c:239 (libqpid-dispatch.so+0xca685)
21: #2 _thread_init /home/travis/build/apache/qpid-dispatch/src/posix/threading.c:172 (libqpid-dispatch.so+0x96f56)
21: #3 <null> <null> (libtsan.so.0+0x2d1af)

21: Mutex M548167088305615232 is already destroyed.

21: SUMMARY: ThreadSanitizer: data race /home/travis/build/apache/qpid-dispatch/src/router_core/connections.c:441 in qdr_connection_process