Make SetupServerArgs callable without NodeContext

bitcoin-gui code needs to call SetupServerArgs but will not have a
NodeContext object if it is communicating with an external bitcoin-node
process.

src/init/bitcoin-node.cpp

@@ -6,6 +6,7 @@
 #include <interfaces/init.h>
 #include <interfaces/ipc.h>
 #include <node/context.h>
+#include <util/system.h>
 
 #include <memory>
 
@@ -20,6 +21,7 @@ public:
         : m_node(node),
           m_ipc(interfaces::MakeIpc(EXE_NAME, arg0, *this))
     {
+        m_node.args = &gArgs;
         m_node.init = this;
     }
     std::unique_ptr<interfaces::Echo> makeEcho() override { return interfaces::MakeEcho(); }