docs: formatdomain: fix incorrect 'Vsock' heading indent
docs: formatdomain: fix incorrect 'Vsock' heading indent

Currently it is visually at the same indent as <seclabel>. This
fixes it to be grouped it with <devices>

Fixes: d4abb7b45d48aba77c2464dbea95f02a43a60834

Reviewed-by: Ján Tomko <4cab11cfb98d3c937327354a78eb07dbb6ee2bc6@redhat.com>
Signed-off-by: Cole Robinson <7cd45ff6ad1fb7cf556a02797d774247851499f8@redhat.com>

olafhering/libvirt,jfehlig/libvirt,jfehlig/libvirt,jardasgit/libvirt,zippy2/libvirt,libvirt/libvirt,nertpinx/libvirt,jardasgit/libvirt,jfehlig/libvirt,zippy2/libvirt,olafhering/libvirt,crobinso/libvirt,crobinso/libvirt,jfehlig/libvirt,crobinso/libvirt,jardasgit/libvirt,libvirt/libvirt,nertpinx/libvirt,jardasgit/libvirt,olafhering/libvirt,olafhering/libvirt,libvirt/libvirt,libvirt/libvirt,jardasgit/libvirt,nertpinx/libvirt,zippy2/libvirt,crobinso/libvirt,nertpinx/libvirt,nertpinx/libvirt,zippy2/libvirt