[network-data] use GetLocator() when registering network data (#4798)

src/core/thread/network_data_leader_ftd.cpp

@@ -52,8 +52,6 @@
 #include "thread/thread_tlvs.hpp"
 #include "thread/thread_uri_paths.hpp"
 
-using ot::Encoding::BigEndian::HostSwap16;
-
 namespace ot {
 namespace NetworkData {
 
@@ -160,8 +158,7 @@ void Leader::HandleServerData(Coap::Message &aMessage, const Ip6::MessageInfo &a
     if (ThreadTlv::GetTlv(aMessage, ThreadTlv::kThreadNetworkData, sizeof(networkData), networkData) == OT_ERROR_NONE)
     {
         VerifyOrExit(networkData.IsValid());
-        RegisterNetworkData(HostSwap16(aMessageInfo.mPeerAddr.mFields.m16[7]), networkData.GetTlvs(),
-                            networkData.GetLength());
+        RegisterNetworkData(aMessageInfo.GetPeerAddr().GetLocator(), networkData.GetTlvs(), networkData.GetLength());
     }
 
     SuccessOrExit(Get<Coap::Coap>().SendEmptyAck(aMessage, aMessageInfo));