daemon: Resolve Coverity FORWARD_NULL
daemon: Resolve Coverity FORWARD_NULL

Coverity complains that the comparison:

  if (nfds && nfds > ((int)!!sock_path + (int)!!sock_path_ro))

could mean 'sock_path' is NULL. Later in virNetSocketNewListenUNIX
there's a direct dereference of path in the error path:

  if (path[0] != '@')

A bit of sleuthing proves that upon entry to daemonSetupNetworking
there is no way for 'sock_path' to be NULL since daemonUnixSocketPaths
will set up 'sock_file' (although it may not set up 'sock_file_ro')
in all 3 paths.

Adjusted code to add ATTRIBUTE_NONNULL(3) on incoming path parameter and
then fixup the comparison of nfds to be a comparison against 2 or 1
depending on whether sock_path_ro is NULL or not.

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