rootlessport: clarify RootlessCNI comment
Update the comment for the RootlessCNI conditional to clarify that
the flag is for rootless bridge networking, not CNI specifically.
The bool is set when netStatus != nil in slirp4netns and will be
removed when slirp4netns and rootlessport are fully dropped.
Signed-off-by: Lokesh Mandvekar <lsm5@redhat.com>