The idea between capabilities and the KVM_CHECK_EXTENSION ioctl is that
userspace can, at run-time, determine if a feature is supported or not.
This allows KVM to being supporting a new feature with a new kernel
version without any need to update user space.  Unfortunately, since the
definition of KVM_CAP_USER_NMI was guarded by #ifdef
__KVM_HAVE_USER_NMI, such discovery still required a user space update.

Therefore, unconditionally export KVM_CAP_USER_NMI and change the
the typo in the comment for the IOCTL number definition as well.
Signed-off-by: NChristoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>