corosync config: support 'linknumber' property

corosync config: support 'linknumber' property

Corosync has moved its rings a layer up, i.e., abstracted away from
the network layer below. That what early were called rings are now
links, knet can have up to 8 all others 1, for now.

Let our parser understand this change in the totem section of the
config, but keep backwards compatibility and accept 'ringnumber'
also.

While we are at it, try to write out the two map operations used in a
bit more readable way.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>