To simplify testing of these rarely used code paths, add a module parameter
that turns it on.  One eventinj.flat test (NMI after iret) fails when
loading kvm_intel with vnmi=0.
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: NRadim Krčmář <rkrcmar@redhat.com>