Fix Heap-use-after-free in MDnsSdListener::Monitor::run

Use thread join to avoid thread exiting after instance
recycled.

Prior to implementing this patch, fuzzing would lead to a segmentation fault after approximately 500 rounds. With the addition of the patch, the fuzzing process can now be repeated for over 30,000 rounds.

Test: m, fuzzing
Fuzzing: mma mdns_service_fuzzer && adb sync data && adb shell /data/fuzz/arm64/mdns_service_fuzzer/mdns_service_fuzzer

Bug: 272382770
Ignore-AOSP-First: Security Issue
(cherry picked from commit 9c0c15f80cffb98b36284dd169a2e62e059dbbe3)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:75e5e2e1faec7aa2812fc6fba30d6fe80558bacd)
Merged-In: I5bc85451b4e6539bad45ceb672924a37952cc138
Change-Id: I5bc85451b4e6539bad45ceb672924a37952cc138