Improve default bundle size and fragment size

If a UDP packet is split into multiple ethernet frames, the entire packet is lost. TCP avoids sending packets larger than an ethernet frame for us, but with a UDP transport, we need to consider the ethernet frame size when configuring UDP.max_bundle_size and FRAG2.frag_size.

Most modern networks should support jumbo frames with 9000 bytes, so we should set UDP.max_bundle_size=8000 and FRAG2.frag_size=8500