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/DnsResolverService.cpp b/DnsResolverService.cpp
index 06f7635..a1efb82 100644
--- a/DnsResolverService.cpp
+++ b/DnsResolverService.cpp
@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
-#define LOG_TAG "DnsResolverService"
+#define LOG_TAG "resolv"
 
 #include "DnsResolverService.h"