Migrate INetd String16 method to std::string

Test: as follows
    - built
    - flashed
    - booted
    - system/netd/tests/runtests.sh passes
Change-Id: I7fe0e14a23b3c6f82dbfa17c7a44d221720976a0
diff --git a/server/NetdNativeService.cpp b/server/NetdNativeService.cpp
index 31a87dc..a3dd980 100644
--- a/server/NetdNativeService.cpp
+++ b/server/NetdNativeService.cpp
@@ -153,12 +153,11 @@
     return binder::Status::ok();
 }
 
-binder::Status NetdNativeService::firewallReplaceUidChain(const android::String16& chainName,
+binder::Status NetdNativeService::firewallReplaceUidChain(const std::string& chainName,
         bool isWhitelist, const std::vector<int32_t>& uids, bool *ret) {
     NETD_LOCKING_RPC(CONNECTIVITY_INTERNAL, gCtls->firewallCtrl.lock);
 
-    android::String8 name = android::String8(chainName);
-    int err = gCtls->firewallCtrl.replaceUidChain(name.string(), isWhitelist, uids);
+    int err = gCtls->firewallCtrl.replaceUidChain(chainName, isWhitelist, uids);
     *ret = (err == 0);
     return binder::Status::ok();
 }