vpn: on Windows force NLMTU on tun interface after creation - #237
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tun.CreateTUNWithRequestedGUID only stores the requested MTU in wireguard-go's internal forcedMTU field — it does not push the value to the Windows IP stack. As a result wintun's default NLMTU of 65535 (WINTUN_MAX_IP_PACKET_SIZE) stays active, local applications see a 65535-byte interface MTU and send oversized packets, which are then silently dropped by the size check in ReadTUNPackets. This broke streaming and P2P apps (Sunshine/Moonlight) on affected machines. Force NLMTU explicitly via winipcfg.IPInterface(family).Set() — the same path the official wireguard-windows tunnel uses. Use a short retry loop because the IP interface row briefly returns ERROR_NOT_FOUND right after adapter creation. Read NLMTU back after Set() and warn on mismatch, to surface third-party LWF filters or Windows 11 MTU regressions that can silently override the value.
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tun.CreateTUNWithRequestedGUID only stores the requested MTU in wireguard-go's internal forcedMTU field — it does not push the value to the Windows IP stack. As a result wintun's default NLMTU of 65535 (WINTUN_MAX_IP_PACKET_SIZE) stays active, local applications see a 65535-byte interface MTU and send oversized packets, which are then silently dropped by the size check in ReadTUNPackets. This broke streaming and P2P apps (Sunshine/Moonlight) on affected machines.
Force NLMTU explicitly via winipcfg.IPInterface(family).Set() — the same path the official wireguard-windows tunnel uses. Use a short retry loop because the IP interface row briefly returns ERROR_NOT_FOUND right after adapter creation. Read NLMTU back after Set() and warn on mismatch, to surface third-party LWF filters or Windows 11 MTU regressions that can silently override the value.
Fixes #236