update documentation of <interface type='hostdev'>
update documentation of <interface type='hostdev'>

<interface type='hostdev' managed='yes'> is supported, but
nowhere mentions 'managed' in <interface type='hostdev'> syntax.
Update documentation to cover it.

Signed-off-by: Chunyan Liu <699809cfcad49bea8cea68d656dfc4a832feaf7a@suse.com>

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