Hold qid->lock when calling deref_portentry() as
socket_search() need portentry to be unchanging.
WARNING: ThreadSanitizer: data race
Write of size 8 at 0x000000000001 by thread T1 (mutexes: write M1):
#0 deref_portentry lib/dns/dispatch.c:630
#1 deactivate_dispsocket lib/dns/dispatch.c:861
#2 udp_recv lib/dns/dispatch.c:1105
#3 udp_exrecv lib/dns/dispatch.c:1028
#4 dispatch lib/isc/task.c:1152
#5 run lib/isc/task.c:1344
#6 <null> <null>
Previous read of size 8 at 0x000000000001 by thread T2 (mutexes: write M1, write M2):
#0 socket_search lib/dns/dispatch.c:661
#1 get_dispsocket lib/dns/dispatch.c:744
#2 dns_dispatch_addresponse lib/dns/dispatch.c:3120
#3 resquery_send lib/dns/resolver.c:2467
#4 fctx_query lib/dns/resolver.c:2217
#5 fctx_try lib/dns/resolver.c:4245
#6 fctx_timeout lib/dns/resolver.c:4570
#7 dispatch lib/isc/task.c:1152
#8 run lib/isc/task.c:1344
#9 <null> <null>(cherry picked from commit 5c253c41)
Closes #2226 (closed)