Create corosync firewall rules independently of localnet

Create corosync firewall rules independently of localnet

"localnet" does not necessarily correspond to the correct network for
corosync (e.g. corosync rings/link can be run independently from other PVE
cluster service networks).

This change uses the previously introduced sub 'for_all_corosync_addresses'
to iterate through all nodes in a corosync cluster and generate rules for
all nodes and all their respective ringX_addr's it finds.

The rules are generated as strict as possible, there is a specific rule
for every remote node and every ring/link. Also, communication "between"
different links/rings is not allowed, e.g. a remote ring1_addr cannot
contact a local ring0_addr, and vice versa.

Multicast is always allowed, for backwards compatibility. Note however,
that we no longer filter on the source of inbound multicast packets,
since that would require localnet, and thus introduce the bug we're
trying to fix once again.

Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>