afs: Show more a bit more server state in /proc/net/afs/servers

Display more information about the state of a server record, including the
flags, rtt and break counter plus the probe state for each server in
/proc/net/afs/servers.

Rearrange the server flags a bit to make them easier to read at a glance in
the proc file.

Signed-off-by: David Howells <dhowells@redhat.com>