Fix -Wimplicit-fallthrough warnings in netd

Test: atest netd_integration_test
Change-Id: Ib5ab9661fb429fdccd6a4c4b5893831ff5fe104e
diff --git a/resolv/res_send.cpp b/resolv/res_send.cpp
index 34a6e18..86db060 100644
--- a/resolv/res_send.cpp
+++ b/resolv/res_send.cpp
@@ -543,9 +543,9 @@
                             /* give the hook another try */
                             if (++loops < 42) /*doug adams*/
                                 break;
-                            /*FALLTHROUGH*/
+                            [[fallthrough]];
                         case res_error:
-                            /*FALLTHROUGH*/
+                            [[fallthrough]];
                         default:
                             goto fail;
                     }
@@ -645,9 +645,9 @@
                             /* give the hook another try */
                             if (++loops < 42) /*doug adams*/
                                 break;
-                            /*FALLTHROUGH*/
+                            [[fallthrough]];
                         case res_error:
-                            /*FALLTHROUGH*/
+                            [[fallthrough]];
                         default:
                             goto fail;
                     }