Obtain a lock on the quota structure.

Obtain a lock on the quota structure.

WARNING: ThreadSanitizer: data race (pid=15228)
  Read of size 4 at 0x7b5c00000444 by thread T8:
    #0 ns_server_status /builds/isc-projects/bind9/bin/named/./server.c:10935:31 (named+0x514671)
    #1 ns_control_docommand /builds/isc-projects/bind9/bin/named/control.c:263:12 (named+0x4e4726)
    #2 control_recvmessage /builds/isc-projects/bind9/bin/named/controlconf.c:465:13 (named+0x4e9046)
    #3 dispatch /builds/isc-projects/bind9/lib/isc/task.c:1157:7 (libisc.so.1107+0x50845)
    #4 run /builds/isc-projects/bind9/lib/isc/task.c:1331:2 (libisc.so.1107+0x4d799)

  Previous write of size 4 at 0x7b5c00000444 by thread T9 (mutexes: write M1082):
    #0 isc_quota_release /builds/isc-projects/bind9/lib/isc/quota.c:73:13 (libisc.so.1107+0x3bf10)
    #1 isc_quota_detach /builds/isc-projects/bind9/lib/isc/quota.c:111:2 (libisc.so.1107+0x3c12b)
    #2 ns_client_endrequest /builds/isc-projects/bind9/bin/named/client.c:896:3 (named+0x4dcad1)
    #3 exit_check /builds/isc-projects/bind9/bin/named/client.c:512:3 (named+0x4d570d)
    #4 ns_client_detach /builds/isc-projects/bind9/bin/named/client.c:3687:8 (named+0x4d7732)
    #5 query_find /builds/isc-projects/bind9/bin/named/query.c (named+0x4f8ff1)
    #6 query_resume /builds/isc-projects/bind9/bin/named/query.c:4164:12 (named+0x509b38)
    #7 dispatch /builds/isc-projects/bind9/lib/isc/task.c:1157:7 (libisc.so.1107+0x50845)
    #8 run /builds/isc-projects/bind9/lib/isc/task.c:1331:2 (libisc.so.1107+0x4d799)