Lock access to state_mctx

Lock access to state_mctx

WARNING: ThreadSanitizer: data race
  Read of size 4 at 0x000000000001 by thread T1 (mutexes: write M1):
    #0 isc___mem_allocate lib/isc/mem.c:1565:2
    #1 isc__mem_allocate lib/isc/mem.c:3048:11
    #2 isc___mem_get lib/isc/mem.c:1304:11
    #3 isc__mem_get lib/isc/mem.c:3012:11
    #4 set_state lib/dns/geoip2.c:174:29
    #5 get_entry_for lib/dns/geoip2.c:236:11
    #6 dns_geoip_match lib/dns/geoip2.c:383:10
    #7 dns_aclelement_match2 lib/dns/acl.c:493:11
    #8 dns_acl_match2 lib/dns/acl.c:298:7
    #9 allowed bin/named/client.c:1866:11
    #10 ns_client_isself bin/named/client.c:1931:7
    #11 notify_isself lib/dns/zone.c:11025:11
    #12 notify_send lib/dns/zone.c:11344:7
    #13 notify_find_address lib/dns/zone.c:11148:2
    #14 zone_notify lib/dns/zone.c:11586:3
    #15 zone_maintenance lib/dns/zone.c:10261:4
    #16 zone_timer lib/dns/zone.c:13106:2
    #17 dispatch lib/isc/task.c:1157:7
    #18 run lib/isc/task.c:1331:2

  Previous write of size 8 at 0x000000000001 by thread T2 (mutexes: write M2, write M3):
    #0 malloc <null>
    #1 internal_memalloc lib/isc/mem.c:887:8
    #2 isc_mem_createx2 lib/isc/mem.c:956:8
    #3 isc_mem_create lib/isc/mem.c:2793:11
    #4 state_key_init lib/dns/geoip2.c:119:14
    #5 get_entry_for lib/dns/geoip2.c:214:11
    #6 dns_geoip_match lib/dns/geoip2.c:383:10
    #7 dns_aclelement_match2 lib/dns/acl.c:493:11
    #8 dns_acl_match2 lib/dns/acl.c:298:7
    #9 allowed bin/named/client.c:1866:11
    #10 ns_client_isself bin/named/client.c:1931:7
    #11 notify_isself lib/dns/zone.c:11025:11
    #12 notify_send lib/dns/zone.c:11344:7
    #13 notify_find_address lib/dns/zone.c:11148:2
    #14 zone_notify lib/dns/zone.c:11586:3
    #15 zone_maintenance lib/dns/zone.c:10261:4
    #16 zone_timer lib/dns/zone.c:13106:2
    #17 dispatch lib/isc/task.c:1157:7
    #18 run lib/isc/task.c:1331:2