I see. Let's see this one: ./yocto_build/tmp/sysroots/clanton/usr/src/kernel/.config
It may be the case that it's not Yocto- or Galileo-specific, what I'd suggest you to do is to look for g_mass_storage driver limitations and general operating conditions, maybe it's not intended for such big file transfers at all? That could help you to determinte the direction of further work - either within Yocto/Galileo (if it's specific to the board) or g_mass_storage driver itself (if it's not intended for such transfers).