Set the dangling pointer to nullptr in the mocked getaddrinfo resolver (#42466)

Test flakiness in proxy_filter_integration_test.cc. Please check
#42217.

The flakiness can not be reproduced, but is showing up in CI
occasionally. Suspecting the ai->ai_next pointer is garbage which caused
the memory leaking and test failure. Explicitly set it to nullptr.

Signed-off-by: Yanjun Xiang <[email protected]>

Author: yanjunxiang-google

test/extensions/filters/http/dynamic_forward_proxy/proxy_filter_integration_test.cc

@@ -37,6 +37,7 @@ class OsSysCallsWithMockedDns : public Api::OsSysCallsImpl {
     ai->ai_addr = reinterpret_cast<sockaddr*>(storage);
     memcpy(ai->ai_addr, addr->sockAddr(), addr->sockAddrLen());
     ai->ai_addrlen = addr->sockAddrLen();
+    ai->ai_next = nullptr;
     return ai;
   }
 

test/extensions/filters/udp/dns_filter/dns_filter_integration_test.cc

@@ -35,6 +35,7 @@ class OsSysCallsWithMockedDns : public Api::OsSysCallsImpl {
     ai->ai_addr = reinterpret_cast<sockaddr*>(storage);
     memcpy(ai->ai_addr, addr->sockAddr(), addr->sockAddrLen());
     ai->ai_addrlen = addr->sockAddrLen();
+    ai->ai_next = nullptr;
     return ai;
   }