afs: Mark address lists with configured priorities

Add a field to each address in an address list (afs_addr_list struct) that
records the current priority for that address according to the address
preference table.  We don't want to do this every time we use an address
list, so the version number of the address preference table is recorded in
the address list too and we only re-mark the list when we see the version
change.

These numbers are then displayed through /proc/net/afs/servers.

Signed-off-by: David Howells <dhowells@redhat.com>
cc: Marc Dionne <marc.dionne@auristor.com>
cc: linux-afs@lists.infradead.org