#395 UDP server relay report sends hardcoded IPGsum placeholder over wire

[Robert McMahon]

Component: src/Reports.c
Function: write_UDP_AckFIN() (sender side, server -> client)
InitServerRelayUDPReport() (receiver side, client)
Introduced: Original 2020 commit (8934a0d0) that added UDP server-side
relay reporting -- this is a long-standing bug, not a regression.
Severity: Low/Medium (cosmetic stat only -- wrong PPS value, no crash,
no data-path impact)
Status: OPEN -- deferred, to be fixed later

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SUMMARY

When a UDP server sends its final stats packet (AckFIN) back to the
client for the enhanced/triptime "Server Report" relay, the wire field
extend.IPGsum is hardcoded:

src/Reports.c, write_UDP_AckFIN():
    hdr->extend.IPGsum = htonl(1);

instead of transmitting the server's real accumulated IPGsum value
(stats->IPGsum, a double, accumulated via TimeDifference() calls between
consecutive packet arrivals in Reporter.c).