isGSOSupported incorrect value on some Android devices

[requilence]

I was debugging issues with slow (or completely stuck) streams on some Android devices that we are experiencing with quic-go in production on anytype. After disabling UDP optimizations by using basicConn, the problems were resolved, so I began investigating different syscalls in sys_conn_oob.go.

isGSOSupported returns true on the problematic device, so I tried to disable it by setting the OS environment variable QUIC_GO_DISABLE_GSO=1, and it helped. According to the Linux manual pages, the UDP_SEGMENT socket option may return 0 if it is disabled. Currently, in the Linux implementation, only the error is checked. This check only verifies whether the Linux kernel recognizes this socket option (kernels >=4.18 should recognize it). The Android device I tested has a kernel version of 4.14.180-perf+, but it appears to recognize this socket option and returns 0.

Also there are no errors on writePacket, so isGSOError is never called.

More device info:

Model: OnePlus 7 Pro (GM1913)
Android version: 12
Kernel version: 4.14.180-perf+
RAM: 8GB
Processor: Qualcomm Snapdragon 855 Octa-core

[requilence]

May be also related to this issue #4169