[Net] ENetMultiplayerPeer now sends fragmented packets unreliably too.

It used to always send them reliably when transfer mode was unreliable
or ordered if the packet size was more then the enet host MTU (1400
bytes by default).

This commit also adds a warning when debug is enabled to explain the
effects of sending fragmented packets unreliably.

modules/enet/enet_multiplayer_peer.cpp

@@ -441,11 +441,11 @@ Error ENetMultiplayerPeer::put_packet(const uint8_t *p_buffer, int p_buffer_size
 	} else {
 		switch (get_transfer_mode()) {
 			case Multiplayer::TRANSFER_MODE_UNRELIABLE: {
-				packet_flags = ENET_PACKET_FLAG_UNSEQUENCED;
+				packet_flags = ENET_PACKET_FLAG_UNSEQUENCED | ENET_PACKET_FLAG_UNRELIABLE_FRAGMENT;
 				channel = SYSCH_UNRELIABLE;
 			} break;
 			case Multiplayer::TRANSFER_MODE_UNRELIABLE_ORDERED: {
-				packet_flags = 0;
+				packet_flags = ENET_PACKET_FLAG_UNRELIABLE_FRAGMENT;
 				channel = SYSCH_UNRELIABLE;
 			} break;
 			case Multiplayer::TRANSFER_MODE_RELIABLE: {
@@ -455,6 +455,12 @@ Error ENetMultiplayerPeer::put_packet(const uint8_t *p_buffer, int p_buffer_size
 		}
 	}
 
+#ifdef DEBUG_ENABLED
+	if ((packet_flags & ENET_PACKET_FLAG_UNRELIABLE_FRAGMENT) && p_buffer_size + 8 > ENET_HOST_DEFAULT_MTU) {
+		WARN_PRINT_ONCE(vformat("Sending %d bytes unrealiably which is above the MTU (%d), this will result in higher packet loss", p_buffer_size + 8, ENET_HOST_DEFAULT_MTU));
+	}
+#endif
+
 	ENetPacket *packet = enet_packet_create(nullptr, p_buffer_size + 8, packet_flags);
 	encode_uint32(unique_id, &packet->data[0]); // Source ID
 	encode_uint32(target_peer, &packet->data[4]); // Dest ID