Missing kvm_create_guest_memfd flag definitions

[valpackett]

Looks like these

#define GUEST_MEMFD_FLAG_MMAP		(1ULL << 0)
#define GUEST_MEMFD_FLAG_INIT_SHARED	(1ULL << 1)

weren't picked up with the ioctl itself (#264).

[roypat]

Hi! Yes, these are a lot more recent than the ioctl, which is why they are not there yet. Have they made it into a linux release yet? Last time I checked, they were just in kvm/next. But if they're in a released linux versions, we'd be happy to accept a PR that updates the bindings to that version!