docs: minor fixes to domain interface documentation
docs: minor fixes to domain interface documentation

A few examples for <interface> had a type='direct' interface with no
sub-elements. This is not allowed - a type='direct' interface must
have at least a source element. (Most likely the example was copied
from the type='user' or type='ethernet' examples - they *do* allow an
instance with no sub-elements).

There was also one place that mistakenly used %lt; ... %gt; instead of
&lt; ... &gt; (for some reason, I make that typo all the time).

bjzhang/libvirt,trainstack/libvirt,trainstack/libvirt,bjzhang/libvirt,zhlcindy/libvirt-1.1.4-maintain,agx/libvirt,rmarwaha/libvirt,rmarwaha/libvirt1,warewolf/libvirt,dumbbell/libvirt,taget/libvirt,VenkatDatta/libvirt,eskultety/libvirt,nertpinx/libvirt,jeckersb/libvirt,olafhering/libvirt,taget/libvirt,emaste/libvirt,andreabolognani/libvirt,VenkatDatta/libvirt,dumbbell/libvirt,crobinso/libvirt,emaste/libvirt,crobinso/libvirt,elmarco/libvirt,jfehlig/libvirt,jardasgit/libvirt,emaste/libvirt,novel/fbsd-libvirt,agx/libvirt,dumbbell/libvirt,novel/fbsd-libvirt,taget/libvirt,rmarwaha/libvirt,warewolf/libvirt,zippy2/libvirt,wiedi/libvirt,siboulet/libvirt-openvz,rlaager/libvirt,libvirt/libvirt,wiedi/libvirt,cbosdo/libvirt,jardasgit/libvirt,agx/libvirt,rmarwaha/libvirt1,cbosdo/libvirt,cbosdo/libvirt,siboulet/libvirt-openvz,olafhering/libvirt,shugaoye/libvirt,rlaager/libvirt,crobinso/libvirt,elmarco/libvirt,nertpinx/libvirt,libvirt/libvirt,jardasgit/libvirt,libvirt/libvirt,rmarwaha/libvirt,dumbbell/libvirt,crobinso/libvirt,andreabolognani/libvirt,nertpinx/libvirt,zippy2/libvirt,bjzhang/libvirt,warewolf/libvirt,datto/libvirt,bjzhang/libvirt,warewolf/libvirt,taget/libvirt,fabianfreyer/libvirt,siboulet/libvirt-openvz,olafhering/libvirt,rlaager/libvirt,trainstack/libvirt,jfehlig/libvirt,trainstack/libvirt,jeckersb/libvirt,zippy2/libvirt,warewolf/libvirt,datto/libvirt,jeckersb/libvirt,taget/libvirt,wiedi/libvirt,warewolf/libvirt,jeckersb/libvirt,datto/libvirt,iam-TJ/libvirt,wiedi/libvirt,zippy2/libvirt,VenkatDatta/libvirt,zhlcindy/libvirt-1.1.4-maintain,andreabolognani/libvirt,shugaoye/libvirt,fabianfreyer/libvirt,libvirt/libvirt,jeckersb/libvirt,siboulet/libvirt-openvz,trainstack/libvirt,shugaoye/libvirt,iam-TJ/libvirt,elmarco/libvirt,iam-TJ/libvirt,cbosdo/libvirt,zhlcindy/libvirt-1.1.4-maintain,rmarwaha/libvirt1,zhlcindy/libvirt-1.1.4-maintain,dumbbell/libvirt,rlaager/libvirt,jfehlig/libvirt,novel/fbsd-libvirt,emaste/libvirt,eskultety/libvirt,novel/fbsd-libvirt,elmarco/libvirt,novel/fbsd-libvirt,iam-TJ/libvirt,jfehlig/libvirt,zhlcindy/libvirt-1.1.4-maintain,rmarwaha/libvirt,novel/fbsd-libvirt,rmarwaha/libvirt,datto/libvirt,trainstack/libvirt,wiedi/libvirt,jardasgit/libvirt,shugaoye/libvirt,rlaager/libvirt,andreabolognani/libvirt,dumbbell/libvirt,olafhering/libvirt,VenkatDatta/libvirt,cbosdo/libvirt,andreabolognani/libvirt,iam-TJ/libvirt,eskultety/libvirt,datto/libvirt,agx/libvirt,elmarco/libvirt,agx/libvirt,jardasgit/libvirt,iam-TJ/libvirt,shugaoye/libvirt,fabianfreyer/libvirt,novel/fbsd-libvirt,wiedi/libvirt,nertpinx/libvirt,eskultety/libvirt,VenkatDatta/libvirt,rmarwaha/libvirt1,emaste/libvirt,jeckersb/libvirt,bjzhang/libvirt,eskultety/libvirt,emaste/libvirt,emaste/libvirt,iam-TJ/libvirt,trainstack/libvirt,novel/fbsd-libvirt,nertpinx/libvirt,rmarwaha/libvirt1,rmarwaha/libvirt,jeckersb/libvirt,novel/fbsd-libvirt,wiedi/libvirt,fabianfreyer/libvirt,siboulet/libvirt-openvz,rmarwaha/libvirt1,warewolf/libvirt,fabianfreyer/libvirt