Split dispatch init/run, join IPv6 multicast discovery group in firmware

firmware/lib/dispatch.cpp

@@ -6,15 +6,17 @@
 #include "timer_queue.h"
 #include "net.h"
 
-[[noreturn]] void dispatch(std::span<const handler_entry> handlers) {
+void dispatch_init() {
+    tusb_init();
+    net_init();
+}
+
+[[noreturn]] void dispatch_run(std::span<const handler_entry> handlers) {
     std::unordered_map<int8_t, void (*)(usb_cdc&, uint32_t)> handler_map;
     for (auto& entry : handlers) {
         handler_map[entry.type_id] = entry.handle;
     }
 
-    tusb_init();
-    net_init();
-
     static usb_cdc usb;
     static timer_queue timers;
     static static_vector<uint8_t, 256> rx_buf;