At least powerpc64 and powerpc64le kernels panic when copyin/copyout
is called by external kernel modules (like pfsync). This patch works
around it while the reason is under investigation.
The panic with exception 0x480 (instruction segment exception) occurs
in a context where the functions are set as pointers in cpuset_copy_cb
struct. It doesn't crash when functions are called directly.
These are ifunc'd functions, so the implementation is decided by a
resolved function at runtime.
MFC after: 1 week