[gn] add build option for TCP (#12134)

This commit adds an option to allow disable building TCP.

etc/gn/openthread.gni

@@ -213,6 +213,9 @@ if (openthread_enable_core_config_args) {
     # Enable SRP Server support
     openthread_config_srp_server_enable = false
 
+    # Enable support for TCP
+    openthread_config_tcp_enable = true
+
     # Enable ping sender support
     openthread_config_ping_sender = false
 

src/core/BUILD.gn

@@ -247,6 +247,8 @@ if (openthread_enable_core_config_args) {
       defines += [ "OPENTHREAD_CONFIG_SRP_SERVER_ENABLE=1" ]
     }
 
+    defines += [ "OPENTHREAD_CONFIG_TCP_ENABLE=${openthread_config_tcp_enable}" ]
+
     if (openthread_config_ping_sender) {
       defines += [ "OPENTHREAD_CONFIG_PING_SENDER_ENABLE=1" ]
     }