Replace res_randomid with arc4random_uniform

Test: built, flashed, booted
      system/netd/tests/runtests.sh pass

Change-Id: Ie1f007f581c7e8becb429c0d27fd1c1b3a3f285e
diff --git a/resolv/res_init.cpp b/resolv/res_init.cpp
index eeafb0c..26cb9f3 100644
--- a/resolv/res_init.cpp
+++ b/resolv/res_init.cpp
@@ -144,7 +144,7 @@
         statp->retrans = RES_TIMEOUT;
         statp->retry = RES_DFLRETRY;
         statp->options = RES_DEFAULT;
-        statp->id = res_randomid();
+        statp->id = arc4random_uniform(65536);
         statp->_mark = MARK_UNSET;
     }