new usermod hooks "onUdpPacket"

this new hooks will help you implement new and custom protocols in
usermods.
I've provided an example (see usermods/udp_name_sync).
The example will help you share the main segment name across different
WLED instances.
The segment name can be useful to sync with some effects like GIF
image or scrolling text.

If you define new packet format in your usermod, make sure it will
either not collide with already used version of wled udp packet :
- 0 is for udp sync
- 1 is for AudioReactive data
- 2 is for udp_name_sync :)

Also, the onUdpPacket will override "parseNotification" if it returns "true".
Have fun!

wled00/um_manager.cpp

@@ -68,6 +68,10 @@ bool UsermodManager::onEspNowMessage(uint8_t* sender, uint8_t* payload, uint8_t
   return false;
 }
 #endif
+bool UsermodManager::onUdpPacket(uint8_t* payload, uint8_t len) {
+  for (auto mod = _usermod_table_begin; mod < _usermod_table_end; ++mod) if ((*mod)->onUdpPacket(payload, len)) return true;
+  return false;
+}
 void UsermodManager::onUpdateBegin(bool init) { for (auto mod = _usermod_table_begin; mod < _usermod_table_end; ++mod) (*mod)->onUpdateBegin(init); } // notify usermods that update is to begin
 void UsermodManager::onStateChange(uint8_t mode) { for (auto mod = _usermod_table_begin; mod < _usermod_table_end; ++mod) (*mod)->onStateChange(mode); } // notify usermods that WLED state changed