summary: sort output by scid per default

The sort order got changed to random(?) I think when cln changed to have
multiple channels per peer supprt.

This restores the old sort by scid order, which is nice since old
channels are upfront.

Maybe we can add other orderings in later commits by copfig options and
`summary` method paramters.

summary/summary.py

@@ -2,6 +2,7 @@
 from pyln.client import Plugin, Millisatoshi
 from packaging import version
 from collections import namedtuple
+from operator import attrgetter
 from summary_avail import trace_availability, addpeer
 import pyln.client
 import requests
@@ -180,7 +181,8 @@ def summary(plugin, exclude=''):
         reply['avail_in'] += ' ({})'.format(to_fiatstr(avail_in))
         reply['fees_collected'] += ' ({})'.format(to_fiatstr(info['fees_collected_msat']))
 
-    if chans != []:
+    if len(chans) > 0:
+        chans = sorted(chans, key=attrgetter('scid'))
         reply['channels_flags'] = 'P:private O:offline'
         reply['channels'] = ["\n"]
         biggest = max(max(int(c.ours), int(c.theirs)) for c in chans)