use smaller mtu for meshnet mode

SSUData.h

@@ -18,7 +18,11 @@ namespace transport
 {
 
 	const size_t SSU_MTU_V4 = 1484;
+	#ifdef MESHNET
+	const size_t SSU_MTU_V6 = 1304;
+	#else
 	const size_t SSU_MTU_V6 = 1472;
+	#endif
 	const size_t IPV4_HEADER_SIZE = 20;
 	const size_t IPV6_HEADER_SIZE = 40;	
 	const size_t UDP_HEADER_SIZE = 8;