net:msg_zerocopy.sh in ubuntu_kernel_selftests flaky on Azure 4.15 (./msg_zerocopy: send: Invalid argument)

[Po-Hsu Lin]

This is not a regression, it's just that this issue was hinted without a bug report.

This issue can be found on instance Standard_B1ms only with:
  * X-Azure-4.15.0-1162.177~16.04.1
  * B-Azure-4.15.0-1162.177
  * B-Azure-4.15.0-1164.179

Test failed with:
 ./msg_zerocopy: send: Connection reset by peer

Test log:
 Running 'make run_tests -C net TEST_PROGS=msg_zerocopy.sh TEST_GEN_PROGS='' TEST_CUSTOM_PROGS='''
 make: Entering directory '/home/azure/autotest/client/tmp/ubuntu_kernel_selftests/src/linux/tools/testing/selftests/net'
 make --no-builtin-rules ARCH=x86 -C ../../../.. headers_install
 make[1]: Entering directory '/home/azure/autotest/client/tmp/ubuntu_kernel_selftests/src/linux'
   CHK include/generated/uapi/linux/version.h
 make[1]: Leaving directory '/home/azure/autotest/client/tmp/ubuntu_kernel_selftests/src/linux'
 TAP version 13
 selftests: msg_zerocopy.sh
 ========================================
 ipv4 tcp -t 1
 cpu: unable to pin, may increase variance.
 cpu: unable to pin, may increase variance.
 rx=36717 (4582 MB)
 ./msg_zerocopy: send: Connection reset by peer
 not ok 1..1 selftests: msg_zerocopy.sh [FAIL]