Unify log tag of DNS resolver

Set LOG_TAG to "resolv" on DNS resolver. Then, the log can be filtered
by "adb logcat [filterspecs]", such as "adb logcat *:S resolv:*", or
'grep'.

Test: resolv_integration_test pass
Change-Id: Ic4f97685d487257560ec3dfe62bab0d187bf9d93
diff --git a/PrivateDnsConfiguration.cpp b/PrivateDnsConfiguration.cpp
index 10f74f9..f4518d4 100644
--- a/PrivateDnsConfiguration.cpp
+++ b/PrivateDnsConfiguration.cpp
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-#define LOG_TAG "PrivateDnsConfiguration"
+#define LOG_TAG "resolv"
 #define DBG 0
 
 #include "PrivateDnsConfiguration.h"