qemuDomainAttachNetDevice: Use 'qemuFDPass' for the vdpa file descriptor
qemuDomainAttachNetDevice: Use 'qemuFDPass' for the vdpa file descriptor

We use the qemuFDPass infrastructure when building the command line,
refactor the monitor too.

Signed-off-by: Peter Krempa <2cf5c04c61aa466e4a47bfedc747d17279c72ffc@redhat.com>
Reviewed-by: Jonathon Jongsma <c7254805a17bd5c41e24c3a278fcbf3afcdfb0fa@redhat.com>
Reviewed-by: Ján Tomko <4cab11cfb98d3c937327354a78eb07dbb6ee2bc6@redhat.com>

zippy2/libvirt,jfehlig/libvirt,crobinso/libvirt,jfehlig/libvirt,zippy2/libvirt,olafhering/libvirt,jfehlig/libvirt,libvirt/libvirt,libvirt/libvirt,zippy2/libvirt,crobinso/libvirt,crobinso/libvirt,libvirt/libvirt,olafhering/libvirt,libvirt/libvirt,jfehlig/libvirt,olafhering/libvirt,crobinso/libvirt,olafhering/libvirt,zippy2/libvirt