fix: update VP_MAX_FRAME_LEN to 1514 to prevent UDP fragmentation

Author: StandartCoder

include/vp_types.h

@@ -15,7 +15,7 @@ enum vp_pkt_type {
 
 // Max VPN payload size (bytes)
 // Limited below full Ethernet MTU to avoid UDP fragmentation.
-#define VP_MAX_FRAME_LEN 1400
+#define VP_MAX_FRAME_LEN 1514
 
 // Max number of connected clients
 #define VP_MAX_CLIENTS 1024