[tmf] use priority message for ServerData and AddressRelease (#7601)

This commit changes to use Thread control traffic priority level
for "Server Data" and "Address Release" TMF messages.
diff --git a/src/core/thread/mle_router.cpp b/src/core/thread/mle_router.cpp
index 7e786ee..6056a21 100644
--- a/src/core/thread/mle_router.cpp
+++ b/src/core/thread/mle_router.cpp
@@ -3671,7 +3671,7 @@
     Tmf::MessageInfo messageInfo(GetInstance());
     Coap::Message *  message;
 
-    VerifyOrExit((message = Get<Tmf::Agent>().NewMessage()) != nullptr, error = kErrorNoBufs);
+    VerifyOrExit((message = Get<Tmf::Agent>().NewPriorityMessage()) != nullptr, error = kErrorNoBufs);
 
     SuccessOrExit(error = message->InitAsConfirmablePost(UriPath::kAddressRelease));
     SuccessOrExit(error = message->SetPayloadMarker());
diff --git a/src/core/thread/network_data.cpp b/src/core/thread/network_data.cpp
index a2e876e..41c1a18 100644
--- a/src/core/thread/network_data.cpp
+++ b/src/core/thread/network_data.cpp
@@ -644,7 +644,7 @@
     Coap::Message *  message = nullptr;
     Tmf::MessageInfo messageInfo(GetInstance());
 
-    VerifyOrExit((message = Get<Tmf::Agent>().NewMessage()) != nullptr, error = kErrorNoBufs);
+    VerifyOrExit((message = Get<Tmf::Agent>().NewPriorityMessage()) != nullptr, error = kErrorNoBufs);
 
     SuccessOrExit(error = message->InitAsConfirmablePost(UriPath::kServerData));
     SuccessOrExit(error = message->SetPayloadMarker());