specfile: require libnl3 for Fedora >= 18 and RHEL >= 7

specfile: require libnl3 for Fedora >= 18 and RHEL >= 7

Everything is ready in both netcf and libvirt to switch over to libnl3
in future releases of both Fedora and RHEL. This needs to be done more
or less simultaneously in both packages, though, because you can't mix
libnl1.1 and libnl3 in the same process (e.g. libvirtd using
libnl-3.so and libnetcf.so, while libnetcf.so uses libnl.so)

This patch does two things when fedora >= 18 || rhel >= 7):

  1) requires libnl3-devel
  2) requires netcf-devel-0.2.2 or greater

(the idea is that a similar patch is going into netcf's specfile, so
that when a build of netcf is done on F18 or later (or RHEL7 or later)
netcf will be guaranteed to be built with libnl3 rather than
libnl-1.1)