KVM: VMX: fix nested vpid for old KVM guests

Old KVM guests invoke single-context invvpid without actually checking
whether it is supported.  This was fixed by commit 518c8aee ("KVM: VMX:
Make sure single type invvpid is supported before issuing invvpid
instruction", 2010-08-01) and the patch after, but pre-2.6.36
kernels lack it including RHEL 6.

Reported-by:  <jmontleo@redhat.com>
Tested-by:  <jmontleo@redhat.com>
Cc: stable@vger.kernel.org
Fixes: 99b83ac8
Reviewed-by: David Matlack <dmatlack@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>