totem: fix check if all nodes have same number of links

configured links may not come in order in the interfaces array, which
holds an entry for _all_ possible links, not just configured ones.

So iterate through all interfaces, but skip those which are not
configured. This allows to start corosync with a configuration where
link 0 is currently not mentioned, as else it was checked but had
member_count = 0 from it's default initialization, which then made
this code report a false positive for the "Not all nodes have the
same number of links" check even on a correct config.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
Reviewed-by: Christine Caulfield <ccaulfie@redhat.com>
Reviewed-by: Jan Friesse <jfriesse@redhat.com>