linux(4): Zero out high order bits of nanoseconds in the compat mode.

Assuming the kernel would use random data, the 64-bit Linux kernel ignores
upper 32 bits of tv_nsec of struct timespec64 for 32-bit binaries.

MFC after: 2 weeks

(cherry picked from commit 1579b320f1a4d555250b82fa74a391d963e7ae13)