Fix stdcopy when reads large frame at once

Fixes TestLogsContainerMuchBiggerThanPage with go 1.3(#6520)
Docker-DCO-1.1-Signed-off-by: Alexandr Morozov <lk4d4math@gmail.com> (github: LK4D4)
Merge pull request #6539 from LK4D4/fix_large_frame_in_stdcopy

Fix stdcopy when reads large frame at once