pub const SCPS_DO_NOT_FRAGMENT: u32 = 0x4000_0000;Expand description
GevSCPSPacketSize bit 30: set do-not-fragment on transmitted packets.
Paired with the test packet so a path that would fragment the datagram drops it instead. Without it a probe can succeed on a link that then delivers reassembled fragments, which is slower than the smaller size it talked us out of.