conf: Report error for unknown shmem ioeventfd value
conf: Report error for unknown shmem ioeventfd value

https://bugzilla.redhat.com/show_bug.cgi?id=1220265

Passing the return value to an enum directly is not safe.  Fix this by
comparing the true integer result of virTristateSwitchTypeFromString().

Signed-off-by: Luyao Huang <23d9981432efa88691fd2a71f5525bc2174f7664@redhat.com>

fabianfreyer/libvirt,fabianfreyer/libvirt,taget/libvirt,zippy2/libvirt,nertpinx/libvirt,taget/libvirt,agx/libvirt,andreabolognani/libvirt,agx/libvirt,agx/libvirt,VenkatDatta/libvirt,rlaager/libvirt,olafhering/libvirt,crobinso/libvirt,agx/libvirt,libvirt/libvirt,andreabolognani/libvirt,jardasgit/libvirt,nertpinx/libvirt,jfehlig/libvirt,olafhering/libvirt,eskultety/libvirt,agx/libvirt,eskultety/libvirt,datto/libvirt,datto/libvirt,zippy2/libvirt,taget/libvirt,libvirt/libvirt,rlaager/libvirt,andreabolognani/libvirt,jardasgit/libvirt,datto/libvirt,libvirt/libvirt,crobinso/libvirt,jardasgit/libvirt,VenkatDatta/libvirt,libvirt/libvirt,nertpinx/libvirt,jardasgit/libvirt,jfehlig/libvirt,crobinso/libvirt,zippy2/libvirt,jfehlig/libvirt,nertpinx/libvirt,andreabolognani/libvirt,VenkatDatta/libvirt,rlaager/libvirt,fabianfreyer/libvirt,eskultety/libvirt,datto/libvirt,nertpinx/libvirt,rlaager/libvirt,eskultety/libvirt,olafhering/libvirt,taget/libvirt,olafhering/libvirt,fabianfreyer/libvirt,jfehlig/libvirt,andreabolognani/libvirt,rlaager/libvirt,fabianfreyer/libvirt,eskultety/libvirt,taget/libvirt,crobinso/libvirt,VenkatDatta/libvirt,jardasgit/libvirt,VenkatDatta/libvirt,datto/libvirt,zippy2/libvirt