Enable -Wsign-compare for netd and fix warnings

Test: atest netd_unit_test netd_integration_test resolv_integration_test
Change-Id: I84347de8f3a3ec0dcc8979037b9c265d145a35f7
diff --git a/server/ResolverController.cpp b/server/ResolverController.cpp
index a0dc3de..39a0b83 100644
--- a/server/ResolverController.cpp
+++ b/server/ResolverController.cpp
@@ -321,7 +321,7 @@
 
     ExternalPrivateDnsStatus privateDnsStatus = {PrivateDnsMode::OFF, 0, {}};
     RESOLV_STUB.resolv_get_private_dns_status_for_net(netId, &privateDnsStatus);
-    for (unsigned i = 0; i < privateDnsStatus.numServers; i++) {
+    for (int i = 0; i < privateDnsStatus.numServers; i++) {
         std::string tlsServer_str = addrToString(&(privateDnsStatus.serverStatus[i].ss));
         tlsServers->push_back(std::move(tlsServer_str));
     }
@@ -418,7 +418,7 @@
         } else {
             dw.println("Private DNS configuration (%u entries)", privateDnsStatus.numServers);
             dw.incIndent();
-            for (unsigned i = 0; i < privateDnsStatus.numServers; i++) {
+            for (int i = 0; i < privateDnsStatus.numServers; i++) {
                 dw.println("%s name{%s} status{%s}",
                            addrToString(&(privateDnsStatus.serverStatus[i].ss)).c_str(),
                            privateDnsStatus.serverStatus[i].hostname,