configure: tweak logic flow of virtport check
configure: tweak logic flow of virtport check

This fixes a small logic bug, where passing --without-macvtap
on the configure line, or otherwise indicating a lack of
support for macvtap, causes configure to bail.

kantai/libvirt-vfork,zippy2/libvirt,datto/libvirt,soulxu/libvirt-xuhj,jeckersb/libvirt,siboulet/libvirt-openvz,shugaoye/libvirt,amery/libvirt-vserver,wiedi/libvirt,dumbbell/libvirt,wiedi/libvirt,leilihh/libvirt,rmarwaha/libvirt1,shugaoye/libvirt,jeckersb/libvirt,usc-isi/libvirt,bjzhang/libvirt,sshah-solarflare/Libvirt-PCI-passthrough-,novel/fbsd-libvirt,emaste/libvirt,warewolf/libvirt,rbu/libvirt,rbu/libvirt,iam-TJ/libvirt,usc-isi/libvirt,sshah-solarflare/Libvirt-PCI-passthrough-,siboulet/libvirt-openvz,emaste/libvirt,datto/libvirt,danwent/libvirt-ovs,wiedi/libvirt,taget/libvirt,usc-isi/libvirt,nertpinx/libvirt,jeckersb/libvirt,rmarwaha/libvirt,olafhering/libvirt,datto/libvirt,warewolf/libvirt,wiedi/libvirt,elmarco/libvirt,fabianfreyer/libvirt,fabianfreyer/libvirt,datto/libvirt,jfehlig/libvirt,libvirt/libvirt,olafhering/libvirt,iam-TJ/libvirt,leilihh/libvirt,danwent/libvirt-ovs,crobinso/libvirt,andreabolognani/libvirt,trainstack/libvirt,eskultety/libvirt,jfehlig/libvirt,rmarwaha/libvirt,elmarco/libvirt,eskultety/libvirt,zhlcindy/libvirt-1.1.4-maintain,andreabolognani/libvirt,warewolf/libvirt,siboulet/libvirt-openvz,amery/libvirt-vserver,trainstack/libvirt,kantai/libvirt-vfork,jeckersb/libvirt,jeckersb/libvirt,fabianfreyer/libvirt,iam-TJ/libvirt,sshah-solarflare/Libvirt-PCI-passthrough-,rlaager/libvirt,nertpinx/libvirt,rmarwaha/libvirt,leilihh/libvirt,novel/fbsd-libvirt,wiedi/libvirt,VenkatDatta/libvirt,zhlcindy/libvirt-1.1.4-maintain,taget/libvirt,dumbbell/libvirt,rmarwaha/libvirt,libvirt/libvirt,zhlcindy/libvirt-1.1.4-maintain,emaste/libvirt,danwent/libvirt-ovs,elmarco/libvirt,VenkatDatta/libvirt,fabianfreyer/libvirt,jeckersb/libvirt,fabianfreyer/libvirt,taget/libvirt,soulxu/libvirt-xuhj,emaste/libvirt,jfehlig/libvirt,foomango/libvirt,agx/libvirt,rlaager/libvirt,novel/fbsd-libvirt,jfehlig/libvirt,foomango/libvirt,rbu/libvirt,nertpinx/libvirt,amery/libvirt-vserver,wiedi/libvirt,foomango/libvirt,leilihh/libvirt,usc-isi/libvirt,zippy2/libvirt,dumbbell/libvirt,eskultety/libvirt,usc-isi/libvirt,nertpinx/libvirt,emaste/libvirt,shugaoye/libvirt,rmarwaha/libvirt1,soulxu/libvirt-xuhj,warewolf/libvirt,zippy2/libvirt,datto/libvirt,cbosdo/libvirt,cbosdo/libvirt,shugaoye/libvirt,iam-TJ/libvirt,rlaager/libvirt,amery/libvirt-vserver,agx/libvirt,novel/fbsd-libvirt,taget/libvirt,zhlcindy/libvirt-1.1.4-maintain,crobinso/libvirt,eskultety/libvirt,rlaager/libvirt,bjzhang/libvirt,eskultety/libvirt,warewolf/libvirt,iam-TJ/libvirt,trainstack/libvirt,libvirt/libvirt,VenkatDatta/libvirt,rmarwaha/libvirt,taget/libvirt,kantai/libvirt-vfork,amery/libvirt-vserver,jardasgit/libvirt,cbosdo/libvirt,trainstack/libvirt,novel/fbsd-libvirt,bjzhang/libvirt,dumbbell/libvirt,emaste/libvirt,cbosdo/libvirt,soulxu/libvirt-xuhj,rmarwaha/libvirt1,sshah-solarflare/Libvirt-PCI-passthrough-,trainstack/libvirt,andreabolognani/libvirt,olafhering/libvirt,bjzhang/libvirt,andreabolognani/libvirt,emaste/libvirt,rbu/libvirt,novel/fbsd-libvirt,novel/fbsd-libvirt,VenkatDatta/libvirt,rmarwaha/libvirt,trainstack/libvirt,leilihh/libvirt,jeckersb/libvirt,danwent/libvirt-ovs,jardasgit/libvirt,jardasgit/libvirt,dumbbell/libvirt,danwent/libvirt-ovs,novel/fbsd-libvirt,nertpinx/libvirt,jardasgit/libvirt,elmarco/libvirt,foomango/libvirt,bjzhang/libvirt,novel/fbsd-libvirt,wiedi/libvirt,rbu/libvirt,soulxu/libvirt-xuhj,crobinso/libvirt,siboulet/libvirt-openvz,agx/libvirt,agx/libvirt,kantai/libvirt-vfork,elmarco/libvirt,kantai/libvirt-vfork,crobinso/libvirt,rmarwaha/libvirt1,cbosdo/libvirt,dumbbell/libvirt,trainstack/libvirt,zippy2/libvirt,warewolf/libvirt,iam-TJ/libvirt,jardasgit/libvirt,warewolf/libvirt,rmarwaha/libvirt1,agx/libvirt,iam-TJ/libvirt,siboulet/libvirt-openvz,libvirt/libvirt,rlaager/libvirt,rmarwaha/libvirt1,VenkatDatta/libvirt,shugaoye/libvirt,andreabolognani/libvirt,leilihh/libvirt,olafhering/libvirt,sshah-solarflare/Libvirt-PCI-passthrough-,zhlcindy/libvirt-1.1.4-maintain,foomango/libvirt