[tcat] add TCAT_ENABLE.req TMF command (#12013)

This adds support for the TMF command to enable TCAT remotely.  A test
is added that uses the 'UDP send' mechanism to send the new TMF
command to a target node.

Some fixes/additions to the test framework are made to support the new
test, including a new argument for udp_send() to send a specific byte
array and udp_rx() to receive data by a UDP client on a node.

src/core/thread/tmf.cpp

@@ -179,6 +179,9 @@ bool Agent::HandleResource(const char *aUriPath, Message &aMessage, const Ip6::M
 #if OPENTHREAD_CONFIG_BACKBONE_ROUTER_DUA_NDPROXYING_ENABLE
         Case(kUriDuaRegistrationRequest, BackboneRouter::Manager);
 #endif
+#endif
+#if OPENTHREAD_CONFIG_BLE_TCAT_ENABLE
+        Case(kUriTcatEnable, MeshCoP::TcatAgent);
 #endif
 
     default: